Can anyone give me a lead for this;

As the audio comes in to drive, the stream itself needs to be encrypted to
be made tamper-proof, not just read-only. If anyone does as much as change a
meta value or cut a sample, it must ring alarm bells. (It's a
security/evidence thing)

I'm not getting far on google with this, have you been here before?

--
dE|_

In article <17FGm.1329$6O1.1097@newsfe08.ams2>, dE|_
 wrote:
> Can anyone give me a lead for this;

> As the audio comes in to drive, the stream itself needs to be encrypted
> to be made tamper-proof, not just read-only. If anyone does as much as
> change a meta value or cut a sample, it must ring alarm bells. (It's a
> security/evidence thing)

You don't say anything about what kind of 'audio' you mean, or what kind of
system the 'drive' is in. That might help.

Nor do you say why what you need could not be done by watermarking the
audio externally to the digital recording process. e.g. by low level ENF.

'As it comes in' would have to be better defined in terms of method. You
could encyrpt on a bit-by-bit or sample-by-sample level against a
max-length sequence or similar. Or use blocks encrypted, etc. The best
choice would depend on what you want and how the system is to be used.

If using a secure system like Unix/Linux then the 'admin' or the specified
user would have to 'know' the encryption keys or equivalent, or at least
have them via shadow, so you can never absolutely guarantee that evidence
has not been tampered with. All you can do is give some level of protection
and detection. You also don't say if those using the machine to record
'audio' should also have the ability to recover the data. i.e. decrypt it.

In forensic terms 'tamper proof' is in practice a relative term, not and
absolute, and also depends on physical chain of evidence handling and the
persons involved operaing in a suitable, documented, manner.

> I'm not getting far on google with this, have you been here before?

Are you a member of the AES? if so you can look at the recent papers in
JAES and conferences about 'forensic audio'. They will give you some ideas
on this, and some individuals you could contact who might advise.
Presumably if you are doing this for professional purposes you would also
be paying for any help.  :-)

Slainte,

Jim

-- 
Please use the address on the audiomisc page if you wish to email me.
Electronics  http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Armstrong Audio  http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc  http://www.audiomisc.co.uk/index.html

"Jim Lesurf" wrote:
>> Can anyone give me a lead for this;
>
>> As the audio comes in to drive, the stream itself needs to be encrypted
>> to be made tamper-proof, not just read-only. If anyone does as much as
>> change a meta value or cut a sample, it must ring alarm bells. (It's a
>> security/evidence thing)
>
> You don't say anything about what kind of 'audio' you mean, or what kind 
> of
> system the 'drive' is in. That might help.
>
> Nor do you say why what you need could not be done by watermarking the
> audio externally to the digital recording process. e.g. by low level ENF.

Sorry, it does not exist yet and the options would be all mine which is why 
I have not specified. Due to the amount there would be, mp3 on hard disk 
would be most practical.

I had thought about watermarking with a slow flanger. What is this ENF you 
speak of?

> 'As it comes in' would have to be better defined in terms of method. You
> could encyrpt on a bit-by-bit or sample-by-sample level against a
> max-length sequence or similar. Or use blocks encrypted, etc. The best
> choice would depend on what you want and how the system is to be used.

I'll look into that, sounds interesting.

> If using a secure system like Unix/Linux then the 'admin' or the specified
> user would have to 'know' the encryption keys or equivalent, or at least
> have them via shadow, so you can never absolutely guarantee that evidence
> has not been tampered with. All you can do is give some level of 
> protection
> and detection. You also don't say if those using the machine to record
> 'audio' should also have the ability to recover the data. i.e. decrypt it.
>
> In forensic terms 'tamper proof' is in practice a relative term, not and
> absolute, and also depends on physical chain of evidence handling and the
> persons involved operaing in a suitable, documented, manner.
>
>> I'm not getting far on google with this, have you been here before?
>
> Are you a member of the AES? if so you can look at the recent papers in
> JAES and conferences about 'forensic audio'. They will give you some ideas
> on this, and some individuals you could contact who might advise.
> Presumably if you are doing this for professional purposes you would also
> be paying for any help.  :-)

There is a chance I could be doing this for professional purposes in the 
future, I'm looking into all the basic options first.

--
dE|_

"Jim Lesurf" asked:
<snip>
> Are you a member of the AES? if so you can look at the recent papers in
> JAES and conferences about 'forensic audio'. They will give you some ideas
> on this, and some individuals you could contact who might advise.

No, I'm not. I'll Google 'forensic audio' next, if you've got any pdfs of 
these papers you could pass on to help with my job challenge just swap 
spambusters with del.

Cheers,

--
dE|_

In article <1dWGm.19944$ei3.9807@newsfe22.ams2>, dE|_
 wrote:

> "Jim Lesurf" wrote:
> >> Can anyone give me a lead for this;

> > Nor do you say why what you need could not be done by watermarking the
> > audio externally to the digital recording process. e.g. by low level
> > ENF.

> Sorry, it does not exist yet and the options would be all mine which is
> why I have not specified. Due to the amount there would be, mp3 on hard
> disk would be most practical.

I suspect you will find that forensic workers would be suspect of lossy
formats like mp3 as they do not represent a full record of the source.
However I can't say more as I don't know enough about the specifics.

They may also want the orginal HD to examine, not just files copied from.
This lets them check the context actually on the disc itself to see if
there are any signs of tampering external to the file payload.

Similarly, they might end up requiring source code for any routines used to
process the recordngs. So open source systems have an advantage here in
evidential terms even if you then have less cover for any aspects you want
to keep commericial in confidence. However I am biassed here. As an
(ex-)academic I regard open source as an inherently more satisfactory
approach to any process which might need to be scrutinised or checked.

> I had thought about watermarking with a slow flanger. What is this ENF
> you speak of?

Electric Network Frequency. In effect, allowing the sound recording to
have a small amount of 'mains hum'. (Which tends to happen anyway, even
when you *don't* want it.  ;-> )

The frequency of mains hum varies with time, and differs from time to time
and with the location (i.e. which mains network covers your area). Hence
it can and has been used as evicence that recordings were recorded when
and where claimed and have no breaks or edits - or not! Bit like an audio
forensic version of dating a tree by its growth rings.  Surprisngly, this
technique has been used a number of times in court, etc, and apparently
works well. Even for recordings made on battery systems where the mics
picked up the hum as interference.


On 31 Oct in uk.rec.audio, dE|_  wrote:

> "Jim Lesurf" asked: <snip>
> > Are you a member of the AES? if so you can look at the recent papers
> > in JAES and conferences about 'forensic audio'. They will give you
> > some ideas on this, and some individuals you could contact who might
> > advise.

> No, I'm not. I'll Google 'forensic audio' next, 

You may find names like Catalin Grigoras, or maybe Koenig and Lacey of BEK
TEK LLC may help. But there may well be others who are more relevant to
what you require. Afraid I can't say for sure as this isn't really my
field. I've only learned about this via casual interest in Journal papers,
etc.[1]

> if you've got any pdfs of these papers you could pass on to help with my
> job challenge just swap spambusters with del.

There are a number of them on the AES website and/or on CDROMs they
supply. Afraid I don't specialise in Forensic Audio so don't have (or know
the contents of) the bulk of them. Hence if you are serious about this I
would recommend membership. Or finding if a local Uni library has JAES at
least. There are also, I think, Journals on Forensic Science that will deal
with such issues. Again a Uni library may help.

If your recordings would be likely end up as court evidence then there is a
great deal involved in establishing that the methods you choose would be
accepted as evidence. Otherwise 'legal eagles' will find all kinds of
excuses for them to be ruled out of consideration. So I'm afraid this isn't
simply a matter of decent engineering and knowing about crypography or
being able to watermark/sign data.

However the levels you'd need to go to would depend on the nature of the
confidence required and the sort of contest the results would be involved
in deciding. Internal arguments within a company could be decided as the
company chose.

Slainte,

Jim

[1] The usual process where you start reading journals and books for one
purpose, only to find you've diverted onto reading something totally
different which seemed interesting when encountered.  :-)

-- 
Please use the address on the audiomisc page if you wish to email me.
Electronics  http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Armstrong Audio  http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc  http://www.audiomisc.co.uk/index.html

"Jim Lesurf" replied to:
>> >> Can anyone give me a lead for this;
>
>> > Nor do you say why what you need could not be done by watermarking the
>> > audio externally to the digital recording process. e.g. by low level
>> > ENF.
>
>> Sorry, it does not exist yet and the options would be all mine which is
>> why I have not specified. Due to the amount there would be, mp3 on hard
>> disk would be most practical.
>
> I suspect you will find that forensic workers would be suspect of lossy
> formats like mp3 as they do not represent a full record of the source.
> However I can't say more as I don't know enough about the specifics.
>
> They may also want the orginal HD to examine, not just files copied from.
> This lets them check the context actually on the disc itself to see if
> there are any signs of tampering external to the file payload.
<snip>

Scrap the mp3 idea, found this baby and the manufacturer is about 5 miles 
from the company who wants the secure recording system.
http://www.cedaraudio.com/products/cambridge/cambridge.html

Also rather than constant recording to mp3 I want to get an auto trigger 
system on this so the uncompressed recording kicks off when a signal comes 
down the line.

--
dE|_

"dE|_"  wrote in message 
news:17FGm.1329$6O1.1097@newsfe08.ams2...
> Can anyone give me a lead for this;
>
> As the audio comes in to drive, the stream itself needs to be encrypted to
> be made tamper-proof, not just read-only. If anyone does as much as change 
> a
> meta value or cut a sample, it must ring alarm bells. (It's a
> security/evidence thing)
>
> I'm not getting far on google with this, have you been here before?
>
> --
> dE|_


Hi dE

You are getting into the area of 'CIA' that is 'Confidentiality', 
'Integrity' and 'Availability'.

Briefly this can be interpreted as:

I want no-one else to read the data.
What I receive at the far end of the media is what was sent.
The data will be available despite any failure of the media and paths from 
send to receive.

If you need to have the audio stream Confidential - i.e. not readable by 
anyone else during transmission, then you will have to encrypt it at source 
before it going onto any transmission media and will have to look at the 
various algorithms for do this.  You also have to consider 'data at rest' 
and 'data in motion'.

The 'Integrity' component will provide the tamper proofing and tamper 
evidence in conjunction with the Confidentiality aspect - again there are 
'at rest' and 'in motion' aspects to this.

Availability is, I think, self evidence and can usually be relied upon by 
the higher levels of the various communication protocols for transmission 
media, but at the application level and physical level involves approaches 
such as RAID, back-up etc..

If you break down your requirements into the above, you should be able to 
find an approach to help you.

Cheers

Mike

"Jim Lesurf"
>
> Electric Network Frequency. In effect, allowing the sound recording to
> have a small amount of 'mains hum'. (Which tends to happen anyway, even
> when you *don't* want it.  ;-> )
>
> The frequency of mains hum varies with time,


** It wanders a small amount, like 0.1%, around the nominal frequency.


> and differs from time to time and with the location (i.e. which mains 
> network covers your area).

** Mains networks cover huge geographical areas, sometimes whole countries - 
within which the frequency is locked in phase.


> Hence
> it can and has been used as evicence that recordings were recorded when
> and where claimed and have no breaks or edits - or not! Bit like an audio
> forensic version of dating a tree by its growth rings.  Surprisngly, this
> technique has been used a number of times in court, etc, and apparently
> works well. Even for recordings made on battery systems where the mics
> picked up the hum as interference.


**  Sure  - you can say if it was in a 50Hz or a 60 Hz country.

    That really narrows things down.



.....  Phil

Jim Lesurf  writes:

<snip>
>
> Slainte,
>
> Jim
>
> [1] The usual process where you start reading journals and books for one
> purpose, only to find you've diverted onto reading something totally
> different which seemed interesting when encountered.  :-)
>
Which is how I came to follow this thread :-)

And the finally I got my act together and looked up "Slainte" and found:
http://www.awa.dk/glosary/slainte.htm

Cheers,

/Martin

"Phil Allison"  wrote in message 
news:7l3vc6F38b20uU1@mid.individual.net...
>
> "Jim Lesurf"
>>
>> Electric Network Frequency. In effect, allowing the sound recording to
>> have a small amount of 'mains hum'. (Which tends to happen anyway, even
>> when you *don't* want it.  ;-> )
>>
>> The frequency of mains hum varies with time,
>
>
> ** It wanders a small amount, like 0.1%, around the nominal frequency.

The tolerance within the EU is +/- 1%. It's unlikely to be much less 
elsewhere.
>
>
>> and differs from time to time and with the location (i.e. which mains 
>> network covers your area).
>
> ** Mains networks cover huge geographical areas, sometimes whole 
> countries - within which the frequency is locked in phase.
>
Even if it only tells you which country it was recorded in, that may well be 
significant.
>
>> Hence
>> it can and has been used as evicence that recordings were recorded when
>> and where claimed and have no breaks or edits - or not! Bit like an audio
>> forensic version of dating a tree by its growth rings.  Surprisngly, this
>> technique has been used a number of times in court, etc, and apparently
>> works well. Even for recordings made on battery systems where the mics
>> picked up the hum as interference.
>
>
> **  Sure  - you can say if it was in a 50Hz or a 60 Hz country.

The difference between 50Hz and 50.5Hz (or even 50.05Hz) is easy to detect 
and measure these days. Discontinuities in the 50Hz waveform, caused by 
editing, can also be readily detected.



David.

"David Looser is FUCKING  MORON "
>
>>
>>> Electric Network Frequency. In effect, allowing the sound recording to
>>> have a small amount of 'mains hum'. (Which tends to happen anyway, even
>>> when you *don't* want it.  ;-> )
>>>
>>> The frequency of mains hum varies with time,
>>
>>
>> ** It wanders a small amount, like 0.1%, around the nominal frequency.
>
> The tolerance within the EU is +/- 1%.


** Got nothing to do with how the frequency  REALLY varies over intervals of 
time like a few minutes.

  Try  MEASURING  it instead of posting  ABSURD   FUCKING   BULLSHIT.

  FUCK  HEAD  !!



>>> and differs from time to time and with the location (i.e. which mains 
>>> network covers your area).
>>
>> ** Mains networks cover huge geographical areas, sometimes whole 
>> countries - within which the frequency is locked in phase.
>>
> Even if it only tells you which country it was recorded in, that may well 
> be significant.

  **  So each country now has its own characteristic mains frequency ??

     When did that happen ????

     ROTFLMAO   !!

    Wot a  fucking   AUTISTIC  MORON  !!!!




>>> Hence
>>> it can and has been used as evicence that recordings were recorded when
>>> and where claimed and have no breaks or edits - or not! Bit like an 
>>> audio
>>> forensic version of dating a tree by its growth rings.  Surprisngly, 
>>> this
>>> technique has been used a number of times in court, etc, and apparently
>>> works well. Even for recordings made on battery systems where the mics
>>> picked up the hum as interference.
>>
>>
>> **  Sure  - you can say if it was in a 50Hz or a 60 Hz country.
>
> The difference between 50Hz and 50.5Hz (or even 50.05Hz) is easy to detect 
> and measure these days.


**  But tells you absolutely NOTHING  -

     YOU   RIDICULOUS   FUCKWIT  !!!




......  Phil

In article , Phil Allison
 wrote:

> "Jim Lesurf"
> >
> > Electric Network Frequency. In effect, allowing the sound recording to
> > have a small amount of 'mains hum'. (Which tends to happen anyway,
> > even when you *don't* want it.  ;-> )
> >
> > The frequency of mains hum varies with time,


> ** It wanders a small amount, like 0.1%, around the nominal frequency.

Yes. The significant point being that if you look in court papers, and
journal papers for the AES and Forensic Science you can see that the
variations with time show patterns that can be reliably used to tell the
date and time recordings were made since many of the details change
unpredictably from day to day.

> > and differs from time to time and with the location (i.e. which mains
> > network covers your area).

> ** Mains networks cover huge geographical areas, sometimes whole
> countries - within which the frequency is locked in phase.

Indeed. And in Europe sometimes cover a series of linked countries.

That is one of the useful features as it means Forensic bodies can monitor
and collect data on the patterns for later comparison with evidential
recordings. As has happened in a number of cases already reported in the
journals.

AES members will have seen papers on this recently. The September 2009
issue of JAES discusses the points I make above. Contains a couple of
papers and a feature article on Audio Forensics. Must admit I was surprised
to read just how useful the technique had turned out to be!

Slainte,

Jim

-- 
Please use the address on the audiomisc page if you wish to email me.
Electronics  http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Armstrong Audio  http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc  http://www.audiomisc.co.uk/index.html

"Phil Allison"  wrote in message 
news:7l5au8F3cdv4dU1@mid.individual.net...
>
>
>     YOU   RIDICULOUS   FUCKWIT  !!!
>

Glad to see that your utterly predicable response arrived promptly. It would 
be a real shame if you were to come up with something new!

:-)

David.

In article , David Looser
 wrote:
> "Phil Allison"  wrote in message
> news:7l3vc6F38b20uU1@mid.individual.net...

> >
> >> and differs from time to time and with the location (i.e. which mains
> >> network covers your area).
> >
> > ** Mains networks cover huge geographical areas, sometimes whole
> > countries - within which the frequency is locked in phase.
> >
> Even if it only tells you which country it was recorded in, that may
> well be significant.

From the published results I've seen in JAES and the accompanying comments
it seems clear it may be able to do far more that that. The key point is
that the pattern of small but measurable changes in frequency isn't the
same every day. So in a manner akin to 'tree rings' you can compare the
pattern with a library of recordings of ENF to find a match. This can then
be a way to tell you which time of day, which day, and in which mains power
network area the recording was made. More usefully it can be used to detect
when parts of a recording have been altered as that tends to cause
localised diversions from the pattern.

> >
> >> Hence it can and has been used as evicence that recordings were
> >> recorded when and where claimed and have no breaks or edits - or not!
> >> Bit like an audio forensic version of dating a tree by its growth
> >> rings.  Surprisngly, this technique has been used a number of times
> >> in court, etc, and apparently works well. Even for recordings made on
> >> battery systems where the mics picked up the hum as interference.
> >
> >
> > **  Sure  - you can say if it was in a 50Hz or a 60 Hz country.

> The difference between 50Hz and 50.5Hz (or even 50.05Hz) is easy to
> detect and measure these days. Discontinuities in the 50Hz waveform,
> caused by editing, can also be readily detected.

Indeed. I must say I was both surprised and impressed by the reports I read
and the data presented on this. I'd known that we could expect variations
duing each day as the load varied. What I hadn't realised was how possible
it was to detect variations in the pattern from one day to another and then
match these with reference ENF pattern records that a forensic body might
collect for such purposes. Quite a neat use of what otherwise people regard
as an annoyance - the tendency for audio recordings to end up with some
background hum.

That said, I must say that the recent JAES paper by the two ex-FBI types
was writting in a stunningly boring way! Presumably to illustrate how
mind-knumbingly legalese reports may need to be written to avoid
nit-picking legal eagles from finding cause for objections!  :-)

Slainte,

Jim

-- 
Please use the address on the audiomisc page if you wish to email me.
Electronics  http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Armstrong Audio  http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc  http://www.audiomisc.co.uk/index.html

"Jim Lesurf"  wrote
>
> From the published results I've seen in JAES and the accompanying comments
> it seems clear it may be able to do far more that that. The key point is
> that the pattern of small but measurable changes in frequency isn't the
> same every day.

I've just tried as an experiment displaying a broadcast TV waveform with the 
'scope timebase locked to the mains frequency. This gives a much more 
immediate indication of mains frequency stability than a frequency meter 
does.

What was noticeable was just how fast mains frequency variations can occur. 
Frequency variations of the order of 0.1% can occur in a matter of seconds, 
an 0.5% variation within a minute or two. I'm sure that the pattern of this 
sort of variation does not conform to a pattern, but is unique on each 
occasion.

David.

David Looser wrote:
> 
> What was noticeable was just how fast mains frequency variations can occur. 
> Frequency variations of the order of 0.1% can occur in a matter of seconds, 
> an 0.5% variation within a minute or two.

http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Frequency/Freq60.htm

When would be the correct time of the day to make perfect speed 
recordings from my synchronous motor powered record deck?


  I'm sure that the pattern of this
> sort of variation does not conform to a pattern, but is unique on each 
> occasion.

It's related to the current appalling state of the weather and what's 
just been suffered through on TV ...

-- 
Adrian C

So, is anyone gonna post a graph of UK mains frequency over a day or
something?

I'd like to see it.

Interesting sub-thread. For a change.


Martin

On Sun, 01 Nov 2009 19:37:28 +0000, Fleetie
 wrote:

>So, is anyone gonna post a graph of UK mains frequency over a day or
>something?
>
>I'd like to see it.
>
>Interesting sub-thread. For a change.
>
>
There is a site that gives that sort of information, unfortunately I
can't find it at the moment, but this site
http://www.dynamicdemand.co.uk/grid.htm  gives you instantaneous
frequency.

On Sun, 01 Nov 2009 19:37:28 +0000, Fleetie
 wrote:

>So, is anyone gonna post a graph of UK mains frequency over a day or
>something?
>
>I'd like to see it.
>
>Interesting sub-thread. For a change.
>
>
>Martin

http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Frequency/Freq60.htm
gives frequency over the last 60 minutes.

Bill Taylor wrote:
> On Sun, 01 Nov 2009 19:37:28 +0000, Fleetie
>  wrote:
> 
>> So, is anyone gonna post a graph of UK mains frequency over a day or
>> something?
>>
>> I'd like to see it.
>>
>> Interesting sub-thread. For a change.
>>
>>
>> Martin
> 
> http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Frequency/Freq60.htm
> gives frequency over the last 60 minutes.

Cool! Thanks!

Martin

In article ,
   Fleetie  wrote:
> So, is anyone gonna post a graph of UK mains frequency over a day or
> something?

Over a day, exactly 50 Hz. For the clocks.

-- 
Small asylum seeker wanted as mud flap, must be flexible and willing to travel

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

"Jim Lesurf uis an Incorrigible LIAR" "
Phil Allison
> "Jim Lesurf"
>> >
>> > Electric Network Frequency. In effect, allowing the sound recording to
>> > have a small amount of 'mains hum'. (Which tends to happen anyway,
>> > even when you *don't* want it.  ;-> )
>> >
>> > The frequency of mains hum varies with time,
>
>
>> ** It wanders a small amount, like 0.1%, around the nominal frequency.
>
> Yes. The significant point being that if you look in court papers, and
> journal papers for the AES and Forensic Science you can see that the
> variations with time show patterns that can be reliably used to tell the
> date and time recordings were made since many of the details change
> unpredictably from day to day.


 **  Shame your post contained NOTHING like that before.

      What a blatant   CHARLATAN   you are.


>> > and differs from time to time and with the location (i.e. which mains
>> > network covers your area).
>
>> ** Mains networks cover huge geographical areas, sometimes whole
>> countries - within which the frequency is locked in phase.
>
> Indeed. And in Europe sometimes cover a series of linked countries.


 **  Which makes you claim above  UTTERLY  STUPID.

     What a blatant   CHARLATAN   you are.


> AES members will have seen papers on this recently. The September 2009
> issue of JAES discusses the points I make above. Contains a couple of
> papers and a feature article on Audio Forensics. Must admit I was 
> surprised
> to read just how useful the technique had turned out to be!


** The technique is basically a load of bollocks.

 Only works if there is a usable hum signal in the recording.

 Only works if the recorder is digital.

 Only checks if the date of the recording is as claimed -  but not the 
location.

 Easily faked by adding a hum signal recorded on another date.

 Legally,  it is 100% worthless.



.....   Phil

"David Looser is FUCKING  MORON "
>
>>
>>> Electric Network Frequency. In effect, allowing the sound recording to
>>> have a small amount of 'mains hum'. (Which tends to happen anyway, even
>>> when you *don't* want it.  ;-> )
>>>
>>> The frequency of mains hum varies with time,
>>
>>
>> ** It wanders a small amount, like 0.1%, around the nominal frequency.
>
> The tolerance within the EU is +/- 1%.


** Got nothing to do with how the frequency  REALLY varies over intervals of
time like a few minutes.

 Try  MEASURING  it instead of posting  ABSURD   FUCKING   BULLSHIT.

 FUCK  HEAD  !!



>>> and differs from time to time and with the location (i.e. which mains 
>>> network covers your area).
>>
>> ** Mains networks cover huge geographical areas, sometimes whole 
>> countries - within which the frequency is locked in phase.
>>
> Even if it only tells you which country it was recorded in, that may well 
> be significant.

 **  So each country now has its own characteristic mains frequency ??

    When did that happen ????

    ROTFLMAO   !!

    Wot a  fucking   AUTISTIC  MORON  !!!!




>>> Hence
>>> it can and has been used as evicence that recordings were recorded when
>>> and where claimed and have no breaks or edits - or not! Bit like an 
>>> audio
>>> forensic version of dating a tree by its growth rings.  Surprisngly, 
>>> this
>>> technique has been used a number of times in court, etc, and apparently
>>> works well. Even for recordings made on battery systems where the mics
>>> picked up the hum as interference.
>>
>>
>> **  Sure  - you can say if it was in a 50Hz or a 60 Hz country.
>
> The difference between 50Hz and 50.5Hz (or even 50.05Hz) is easy to detect 
> and measure these days.


**  But tells you absolutely NOTHING  -

     YOU   RIDICULOUS   FUCKWIT  !!!



......  Phil

"Jim Lesurf is 100% FULL OF BULLSHIT "
>
 > David Loser is a totally autistic pommy Shit Head
>
> "Phil Allison"
>> >
>> >> and differs from time to time and with the location (i.e. which mains
>> >> network covers your area).
>> >
>> > ** Mains networks cover huge geographical areas, sometimes whole
>> > countries - within which the frequency is locked in phase.
>> >
>> Even if it only tells you which country it was recorded in, that may
>> well be significant.
>
> From the published results I've seen in JAES and the accompanying comments
> it seems clear it may be able to do far more that that.

**  That is  ABSOLUTE  BOLLOCKS  !!


> The key point is
> that the pattern of small but measurable changes in frequency isn't the
> same every day. So in a manner akin to 'tree rings' you can compare the
> pattern with a library of recordings of ENF to find a match. This can then
> be a way to tell you which time of day, which day, and in which mains 
> power
> network area the recording was made.

**  That last bit is  ABSOLUTE  BOLLOCKS.


> More usefully it can be used to detect
> when parts of a recording have been altered as that tends to cause
> localised diversions from the pattern.

**  A fake hum can easily be added to cover the existence of edits.

     What a stupid and legally worthless idea.


>> > **  Sure  - you can say if it was in a 50Hz or a 60 Hz country.
>
>> The difference between 50Hz and 50.5Hz (or even 50.05Hz) is easy to
>> detect and measure these days. Discontinuities in the 50Hz waveform,
>> caused by editing, can also be readily detected.
>
> Indeed.

** A fake hum can easily be added to cover the existence of edits.

     What a stupid and legally worthless idea.



.....  Phil

"Fleetie the Freakoid "
>
> So, is anyone gonna post a graph of UK mains frequency over a day or
> something?
>
> I'd like to see it.


** Retarded fuckwits like Fleetie stare at wallpaper for hours on end too.

  Then maybe take a 10 minute break to watch grass grow.

  LOL  !!



....   Phil

"Bill Taylor"

> http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Frequency/Freq60.htm
> gives frequency over the last 60 minutes.


**  Backs up my comments  PRECISELY .

    Typical deviations are in the order of 0.1%.



....   Phil

"Fleetie the Freakoid "


>> http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Frequency/Freq60.htm
>> gives frequency over the last 60 minutes.
>
> Cool! Thanks!
>

**  Hey  -  there is a fly crawling up the wall  !!

    Better keep your eyes locked on it  ....




....   Phil

In article , Adrian C
<email@here.invalid> wrote:
> David Looser wrote:
> > 
> > What was noticeable was just how fast mains frequency variations can
> > occur. Frequency variations of the order of 0.1% can occur in a
> > matter of seconds, an 0.5% variation within a minute or two.

> http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Frequency/Freq60.htm

> When would be the correct time of the day to make perfect speed
> recordings from my synchronous motor powered record deck?

That would depend on the clocking of the recorder as well as the speed of
the turntable. If they both uses the mains then you may be fine - ignoring
the effects on any equalisation. :-)

However if you are concerned to get stable TT rotation, then the logical
approach is to use a motor driven by its own clock, and not to rely on
mains frequency. I've used a direct drive TT for decades which uses its own
internal clock. And I think you can buy PSUs for TTs that generate '50Hz
mains' from an internal clock.

I recall having an argument...  erm discussion with someone decades ago. He
was saying his TT was a superior design as it used the same clock for both
driving the TT and the strobe which let you check rotation speed.  Gave the
system perfect performance. Hmmm....  :-)

Oh, and you may find that 'rubber band drive' for a TT will give you
changes in rotation speed as the loudness of the music changes.  :-)

>   I'm sure that the pattern of this
> > sort of variation does not conform to a pattern, but is unique on each
> > occasion.

> It's related to the current appalling state of the weather and what's
> just been suffered through on TV ...

...and the rain it raineth every day... somewhere.

Slainte,

Jim

-- 
Please use the address on the audiomisc page if you wish to email me.
Electronics  http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Armstrong Audio  http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc  http://www.audiomisc.co.uk/index.html

Tell you what, I can remember looking at such things when I could see and I 
was young enough not to worry about being thrown across the room  that the 
noise, even then, on the mains was awful, not only that, but the apparent 
lop sided sine wave was a bit worrying as well.

Why do you ask anyway, I doubt it matter so much these days, given the 
switch mode supplies etc.

Brian

-- 
Brian Gaff - briang1@blueyonder.co.uk
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"Fleetie"  wrote in message 
news:_Y2dnTBK5YPkfnDXnZ2dnUVZ8kNi4p2d@bt.com...
> So, is anyone gonna post a graph of UK mains frequency over a day or
> something?
>
> I'd like to see it.
>
> Interesting sub-thread. For a change.
>
>
> Martin

"Brian Gaff"  wrote in message 
news:p_yHm.889$Ym4.726@text.news.virginmedia.com...

> Tell you what, I can remember looking at such things when I could see and 
> I was young enough not to worry about being thrown across the room

By an electric shock do you mean?. Being thrown across the room is something 
that can happen with a shock from DC, unlikely with AC.

> noise, even then, on the mains was awful, not only that, but the apparent 
> lop sided sine wave was a bit worrying as well.

I'm not sure of the relevance of this to the discussion. Anyway by 
"lopsided" do you mean that the even-order harmonic distortion was so bad 
that it was very obvious on an oscilloscope?, if so I ask how you were 
connecting the mains to the 'scope. I suspect that this distortion was 
caused by something local to you, harmonic distortion on the mains is 
normally mainly odd-order.
>
> Why do you ask anyway, I doubt it matter so much these days, given the 
> switch mode supplies etc.
>
The question originally arose as part of a discussion on "watermarking" 
audio recordings by the use of mains hum. It has since widened to talking 
about speed variation on turntables using mains-synchronous motors. SMPSs 
are irrelevant to this.

David.

"Jim Lesurf"

> I recall having an argument...  erm discussion with someone decades ago. 
> He
> was saying his TT was a superior design as it used the same clock for both
> driving the TT and the strobe which let you check rotation speed.  Gave 
> the
> system perfect performance. Hmmm....  :-)


** Much funnier is the hi-fi dude who insisted his " Quartz Locked DD " 
turntable was imperfect cos the strobe neon showed a slow drift in one 
direction or other when then TT was supposedly locked on exact speed.

:-0 ..........................



.....    Phil

"Phil Allison"  wrote in message 
news:7l6pn2F3bs4ssU1@mid.individual.net...
>
> "David Looser is FUCKING  MORON "
>>
>>>
>>>> Electric Network Frequency. In effect, allowing the sound recording to
>>>> have a small amount of 'mains hum'. (Which tends to happen anyway, even
>>>> when you *don't* want it.  ;-> )
>>>>
>>>> The frequency of mains hum varies with time,
>>>
>>>
>>> ** It wanders a small amount, like 0.1%, around the nominal frequency.
>>
>> The tolerance within the EU is +/- 1%.
>
>
> ** Got nothing to do with how the frequency  REALLY varies over intervals 
> of
> time like a few minutes.
>
> Try  MEASURING  it instead of posting  ABSURD   FUCKING   BULLSHIT.
>
> FUCK  HEAD  !!
>
>
>
>>>> and differs from time to time and with the location (i.e. which mains 
>>>> network covers your area).
>>>
>>> ** Mains networks cover huge geographical areas, sometimes whole 
>>> countries - within which the frequency is locked in phase.
>>>
>> Even if it only tells you which country it was recorded in, that may well 
>> be significant.
>
> **  So each country now has its own characteristic mains frequency ??
>
>    When did that happen ????
>
>    ROTFLMAO   !!
>
>    Wot a  fucking   AUTISTIC  MORON  !!!!
>
>
>
>
>>>> Hence
>>>> it can and has been used as evicence that recordings were recorded when
>>>> and where claimed and have no breaks or edits - or not! Bit like an 
>>>> audio
>>>> forensic version of dating a tree by its growth rings.  Surprisngly, 
>>>> this
>>>> technique has been used a number of times in court, etc, and apparently
>>>> works well. Even for recordings made on battery systems where the mics
>>>> picked up the hum as interference.
>>>
>>>
>>> **  Sure  - you can say if it was in a 50Hz or a 60 Hz country.
>>
>> The difference between 50Hz and 50.5Hz (or even 50.05Hz) is easy to 
>> detect and measure these days.
>
>
> **  But tells you absolutely NOTHING  -
>
>     YOU   RIDICULOUS   FUCKWIT  !!!

And to think I was going to run the radio reception board through a 
white/pink noise filter before recording : (

--
dE|_

"dE|_" 


   RIDICULOUS   FUCKWIT  !!!
>
> And to think I was going to run the radio reception board through a 
> white/pink noise filter before recording : (



**  I this retarded fuck on stale 1960s  LSD ??

   White / pink noise   FILTER ???





....  Phil

"Phil Allison"  wrote in message 
news:7l80leF3bosaoU1@mid.individual.net...
>
> "dE|_" 
>
>
>   RIDICULOUS   FUCKWIT  !!!
>>
>> And to think I was going to run the radio reception board through a 
>> white/pink noise filter before recording : (
>
>
>
> **  I this retarded fuck on stale 1960s  LSD ??
>
>   White / pink noise   FILTER ???

Have you got a bald head and tatoos of guns & barbed wire?

I'll leave you lot to it & stick with the other lot who are actually 
discussing rather than throwing bottles at eachother.

--
dE|_

"dE|_usional "
>
>
>>   RIDICULOUS   FUCKWIT  !!!
>>>
>>> And to think I was going to run the radio reception board through a 
>>> white/pink noise filter before recording : (
>>
>>
>>
>> **  I this retarded fuck on stale 1960s  LSD ??
>>
>>   White / pink noise   FILTER ???
>
> Have you got a bald head and tatoos of guns & barbed wire?
>
> I'll leave you lot to it & stick with the other lot who are actually 
> discussing rather than throwing bottles at eachother.


** Your original Q was beyond absurd  -  requiring a major invention for a 
solution.

If anyone ever thought of one,  the * LAST * thing they would do is post it 
to a steaming,  great  DELUSIONAL  FUCKWIT like you on a fucking stupid news 
group.

Capice  ??



...   Phil

"David Looser"  wrote in
message news:7l5vcjF3b3vjmU1@mid.individual.net
> "Jim Lesurf"  wrote
>>
>> From the published results I've seen in JAES and the
>> accompanying comments it seems clear it may be able to
>> do far more that that. The key point is that the pattern
>> of small but measurable changes in frequency isn't the
>> same every day.
>
> I've just tried as an experiment displaying a broadcast
> TV waveform with the 'scope timebase locked to the mains
> frequency. This gives a much more immediate indication of
> mains frequency stability than a frequency meter does.

IME the world is now full of devices that have what used to be exceptionally 
stable frequency and time-base stability. Spend the big bucks on a frequency 
counter, and can you get quite a piece of work. Spend less bucks, and you'll 
still get something that is very stable if you keep its temperature and 
power line voltage stable and don't move it around too much.

> What was noticeable was just how fast mains frequency
> variations can occur. Frequency variations of the order
> of 0.1% can occur in a matter of seconds, an 0.5%
> variation within a minute or two. I'm sure that the
> pattern of this sort of variation does not conform to a
> pattern, but is unique on each occasion.

Similar things are noticable in the US.  If you use a good high-resolution 
frequency counter to measure the mains frequency, the low-order digits 
(which should be and are stable if you monitor a more reliable source) will 
"wander around".

OTOH, the long-term averages, are generally very good. Power-line operated 
clocks are very stable as long as power is not totally interrupted.  In the 
50s and 60s it was thought that the power in Europe was not as stable as 
that in the US, but I don't know why that would be true today.

I've always presumed that the variations were due to  variations in loading 
which we know happens.  However, hypothesizing how this would actually 
happen from a theoretical standpoint is something that I've found 
challenging.

"Arny Krueger"
>
>
> I've always presumed that the variations were due to variations in loading 
> which we know happens.  However, hypothesizing how this would actually 
> happen from a theoretical standpoint is something that I've found 
> challenging.


** What mysterious agency does Arny imagine cause the massive alternators 
inside power stations to spin in first place ??

  Something quite Satanic,  no doubt.



....  Phil

"Phil Allison"  wrote in message
news:7l887cF3bv1kuU1@mid.individual.net
> "Arny Krueger"
>>
>>
>> I've always presumed that the variations were due to
>> variations in loading which we know happens.  However,
>> hypothesizing how this would actually happen from a
>> theoretical standpoint is something that I've found
>> challenging.

> ** What mysterious agency does Arny imagine cause the
> massive alternators inside power stations to spin in
> first place ??

I'm thinking water, steam, diesel, and/or air depending...

However, most of these things seem to be the sort of thing that spins with 
relatively few short-term variations. And, if any individual one of them 
were much out-of-phase, the circulating currents could be pretty massive. I 
therefore presume that the operations staffs minimize them.

Dave Plowman (News) wrote:
> In article ,
>    Fleetie  wrote:
>> So, is anyone gonna post a graph of UK mains frequency over a day or
>> something?
> 
> Over a day, exactly 50 Hz. For the clocks.
> 
Yeah thanks Dave. Bleedin' obvious.

That could come about from swings as wide as +/- 5Hz, 0.5Hz, or 0.05Hz.

I wanted to see what kind of variation was typical, and over what
timescales it changes.

"Exactly 50Hz over a day" indeed! Have you got that PhD in the bleedin'
obvious framed in your hall?


Sheesh.


Martin >:-/

"Arny Krueger"
> "Phil Allison"
>>
>>>
>>> I've always presumed that the variations were due to
>>> variations in loading which we know happens.  However,
>>> hypothesizing how this would actually happen from a
>>> theoretical standpoint is something that I've found
>>> challenging.
>
>> ** What mysterious agency does Arny imagine cause the
>> massive alternators inside power stations to spin in
>> first place ??
>
> I'm thinking water, steam, diesel, and/or air depending...
>
> However, most of these things seem to be the sort of thing that spins with 
> relatively few short-term variations.

** The rpms are controlled by continually adjusting the steam pressure or 
water flow to a turbine. A feedback control loop is involved to hold 
alternator rpms close as possible to nominal.

A counter keeps track of the number of revolutions over longer periods, 
making fine adjustments to the rpm to make sure clocks will alway be 
accurate.


> And, if any individual one of them were much out-of-phase, the circulating 
> currents could be pretty massive. I therefore presume that the operations 
> staffs minimize them.

** Any alternator that is not being driven simply becomes a synchronous 
motor, it spins at the same rpm as all the others but draws current instead 
of supplying it. Its rotor will have a small phase lag compared to the 
others.

My information is that hydro power stations have the shortest response times 
to load changes - so they are generally used as the pace setters for a 
network involving steam ( ie coal, oil or nuke) stations.


.....  Phil

"Phil Allison"  wrote in message
news:7l9bcuF3dciraU1@mid.individual.net
>
> My information is that hydro power stations have the
> shortest response times to load changes - so they are
> generally used as the pace setters for a network
> involving steam ( ie coal, oil or nuke) stations.

I have friends in the biz, and that is what they say.  Hydro power levels 
can be altered almost as easily as  turning a spigot. I spent my vacation 
canoeing and hiking along the Manistee River in Michigan, which is 
downstream of an active power dam. Its flow and water level was changing 
constantly, and in very unnatural ways.

The larger coal and nuke stations can't start themselves and need a 
partially operational power net to start them up.