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How can I tell music has been an MP3? Quantitative Measurement of Fidelity



 
 
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  #1  
Old June 22nd 07, 11:18 PM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
Dave
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Posts: 8
Default How can I tell music has been an MP3? Quantitative Measurement of Fidelity

I have been disappointed with the audio quality of some CDs I have
bought recently. Is there a free program I can use to get an accepted
measurement of fidelity? (like a signal to noise ratio)

I have my suspicious that some may have been stored an MP3s and then
"unripped" in the factory. So how can I tell for certain if my CD has
been an MP3, or other lossy format? I'd hope mp3 storage would leave
different markers than the original tape, for example.

To get a good measure I'd expect some Fourier transforms and signal
analysis to be done, so this should be relevant to sci.physics.

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  #2  
Old June 22nd 07, 11:26 PM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
[email protected]
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Posts: 402
Default How can I tell music has been an MP3? Quantitative Measurement of Fidelity

On Jun 22, 6:18 pm, Dave > wrote:
> I have been disappointed with the audio quality of some CDs I have
> bought recently. Is there a free program I can use to get an accepted
> measurement of fidelity? (like a signal to noise ratio)
>
> I have my suspicious that some may have been stored an MP3s and then
> "unripped" in the factory. So how can I tell for certain if my CD has
> been an MP3, or other lossy format? I'd hope mp3 storage would leave
> different markers than the original tape, for example.


There's no particularly good reason why the "factory"
would want to do such a things.

There's a far more mundane explanation. Recent
music distribution, including CDs, have suffered
from an industry-wide of sever over compression,
limiting and clipping, as an endemic result of the
mastering process. There's been this headlong
to produce "louder and louder" CDs. Many producers
have decided, quite incorrectly, to equate louder
with better.

The result is a dramatic deterioration of available
music,especially in the pop music genres. It
has nothing to do with MP3, it has everything to
do with overall incompetence and disregard of high
production standards.

> To get a good measure I'd expect some Fourier transforms and signal
> analysis to be done, so this should be relevant to sci.physics.


Nope, simply any peak-to-average measurement
should reveal an overl trend in this direction over the
last decade or so.

  #3  
Old June 22nd 07, 11:54 PM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
Richard Crowley
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Posts: 4,172
Default How can I tell music has been an MP3? Quantitative Measurement of Fidelity

"Dave" wrote ...
>I have been disappointed with the audio quality of some CDs I have
> bought recently.


This has been discussed many times in the recent past.
Note that far and away the prime suspect is hyper-compression
(compression of the audio levels, NOT data compression of the
signal stream.)

> Is there a free program I can use to get an accepted
> measurement of fidelity? (like a signal to noise ratio)


1) SNR is not "an accepted measurement of fidelity"
2) There is no specific "accepted measurement of fidelity"
"Fidelity" is a combination of many things. Some subjective.
3) It would be difficult-to-impossible to actually meausre SNR
on a commercial CD because of the way they are mastered.
(i.e. there is no "baseline" because it is usually muted)

> I have my suspicious that some may have been stored an MP3s and then
> "unripped" in the factory. So how can I tell for certain if my CD has
> been an MP3, or other lossy format? I'd hope mp3 storage would leave
> different markers than the original tape, for example.


Did you buy these CDs from the back of Guido's white van?
Do you know they are legitimate and not pirated copies?
Seems very unlikely that commercial CDs would have ever been
processed through any such gross lossy step as MP3 compression.

> To get a good measure I'd expect some Fourier transforms and signal
> analysis to be done, so this should be relevant to sci.physics.


It has been discussed here before that there are relatively easy ways
of analyzing audio to detect lossy compression such as MP3. Many
people claim they can hear it easily.


  #4  
Old June 23rd 07, 02:58 AM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
Dave
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Posts: 8
Default How can I tell music has been an MP3? Quantitative Measurement of Fidelity

On 22 Jun, 23:54, "Richard Crowley" > wrote:
> "Dave" wrote ...
>
> >I have been disappointed with the audio quality of some CDs I have
> > bought recently.

>
> This has been discussed many times in the recent past.
> Note that far and away the prime suspect is hyper-compression
> (compression of the audio levels, NOT data compression of the
> signal stream.)
>
> > Is there a free program I can use to get an accepted
> > measurement of fidelity? (like a signal to noise ratio)

>
> 1) SNR is not "an accepted measurement of fidelity"
> 2) There is no specific "accepted measurement of fidelity"
> "Fidelity" is a combination of many things. Some subjective.
> 3) It would be difficult-to-impossible to actually meausre SNR
> on a commercial CD because of the way they are mastered.
> (i.e. there is no "baseline" because it is usually muted)

Have there been no bright PhD students sponsored by the music
industry, or are they too busy with their revenue stream? The noise
is what is not the notes. For a symphony you have an idea of what the
notes should be, because you have the sheet music, and you know what a
violin, flute etc should sound like. You may be able to measure
something more because that is what the brain does.
>
> > I have my suspicious that some may have been stored an MP3s and then
> > "unripped" in the factory. So how can I tell for certain if my CD has
> > been an MP3, or other lossy format? I'd hope mp3 storage would leave
> > different markers than the original tape, for example.

>
> Did you buy these CDs from the back of Guido's white van?
> Do you know they are legitimate and not pirated copies?
> Seems very unlikely that commercial CDs would have ever been
> processed through any such gross lossy step as MP3 compression.

Business takes the route of maximum profit.
>
> > To get a good measure I'd expect some Fourier transforms and signal
> > analysis to be done, so this should be relevant to sci.physics.

>
> It has been discussed here before that there are relatively easy ways
> of analyzing audio to detect lossy compression such as MP3. Many
> people claim they can hear it easily.

The method I saw was looking for high frequency cut off. Is this was
you were thinking of?

  #5  
Old June 23rd 07, 03:43 AM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
Richard Crowley
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Posts: 4,172
Default How can I tell music has been an MP3? Quantitative Measurement of Fidelity

"Dave" wrote ...
> , "Richard Crowley" wrote:


>> 1) SNR is not "an accepted measurement of fidelity"
>> 2) There is no specific "accepted measurement of fidelity"
>> "Fidelity" is a combination of many things. Some subjective.
>> 3) It would be difficult-to-impossible to actually meausre SNR
>> on a commercial CD because of the way they are mastered.
>> (i.e. there is no "baseline" because it is usually muted)


> Have there been no bright PhD students sponsored by the music
> industry, or are they too busy with their revenue stream? The noise
> is what is not the notes. For a symphony you have an idea of what the
> notes should be, because you have the sheet music, and you know what a
> violin, flute etc should sound like. You may be able to measure
> something more because that is what the brain does.


That is just impossibly simplistic. There is a great deal of stuff
"between the notes" besides noise. Have you done much
recording yourself?

>> > I have my suspicious that some may have been stored an MP3s and then
>> > "unripped" in the factory. So how can I tell for certain if my CD has
>> > been an MP3, or other lossy format? I'd hope mp3 storage would leave
>> > different markers than the original tape, for example.

>>
>> Did you buy these CDs from the back of Guido's white van?
>> Do you know they are legitimate and not pirated copies?
>> Seems very unlikely that commercial CDs would have ever been
>> processed through any such gross lossy step as MP3 compression.


> Business takes the route of maximum profit.


If you dont' want to reveal any clues that would help answer
your question, its up to you.

>> > To get a good measure I'd expect some Fourier transforms and signal
>> > analysis to be done, so this should be relevant to sci.physics.

>>
>> It has been discussed here before that there are relatively easy ways
>> of analyzing audio to detect lossy compression such as MP3. Many
>> people claim they can hear it easily.


> The method I saw was looking for high frequency cut off. Is this was
> you were thinking of?


No, there are supposed to be other "markers" of MP3-style compression.
But I didn't pay attention to what they were or how to find them because I'm
not particularly concerned. I use MP3 only as a last-step release format.


  #6  
Old June 23rd 07, 04:36 AM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
Rich[_2_]
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Posts: 2
Default How can I tell music has been an MP3? Quantitative Measurementof Fidelity

Dave wrote:
> I have been disappointed with the audio quality of some CDs I have
> bought recently. Is there a free program I can use to get an accepted
> measurement of fidelity? (like a signal to noise ratio)


Some famous commercial recordings have a low s/n being recorded at
home. I had assumed my cassette tape (forget which song now) was
bad till years later when I bought a CD and it sounded the same.

A few issues ago Maximum PC did a comparison among lossless codecs
and at 192 kb/s there was only one track where any difference could
be heard. Now mp3 is a lossy codec, but at higher bitrates I doubt
there is much difference in the sound. For mp3's I suspect that
256 kb/s is where you'll have difficulty telling the difference.

> I have my suspicious that some may have been stored an MP3s and then
> "unripped" in the factory.


Long ago I made a custom CD for my wife's aunt and I ripped wav files
from her CD's and remastered the tracks she wanted. She was very pleased
with the results.

Less long ago she wanted another CD. I had forgotten where I put them
and when I found them this time I ripped mp3's at 128 kb/s and remastered
the CD, she was very disappointed with the quality this time. As I recall
I needed to free up some disk space at that time so this seemed quickest.
But obviously mp3's are not as good as the original wav files.

> So how can I tell for certain if my CD has
> been an MP3, or other lossy format? I'd hope mp3 storage would leave
> different markers than the original tape, for example.


There may be another way, there is a public database of CD's, immdb
or something like that. I'm not sure how they identify the CD, perhaps
the volume name, but I suggest that any casually remastered CD, or
any made from mp3's from the net won't have the same volume name, or
whatever they use. That is, I suggest you rip the tracks from the
CD with some software that can identify the disk from immdb, if it
cannot identify the CD, there's a good chance it's as you suspect.
Unless you've for some obscure latin CD or something, the database
is not complete, but for any popular release this should work. I
think Nero will do this, I've not done it for years though.

Note, you don't have to rip the tracks, just see if the CD can
be identified.

Cheers,

Rich


> To get a good measure I'd expect some Fourier transforms and signal
> analysis to be done, so this should be relevant to sci.physics.
>

  #7  
Old June 23rd 07, 06:44 AM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
Colin B.
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Posts: 29
Default How can I tell music has been an MP3? Quantitative Measurement of Fidelity

In rec.audio.tech Dave > wrote:
> I have been disappointed with the audio quality of some CDs I have
> bought recently. Is there a free program I can use to get an accepted
> measurement of fidelity? (like a signal to noise ratio)
>
> I have my suspicious that some may have been stored an MP3s and then
> "unripped" in the factory. So how can I tell for certain if my CD has
> been an MP3, or other lossy format? I'd hope mp3 storage would leave
> different markers than the original tape, for example.


Unless these are pirated copies, the answer is most likely not. That's
too much pointless effort for commercial studios to go through.

The answer is much more mundane: Most recording sucks.

  #9  
Old June 23rd 07, 07:30 AM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
[email protected]
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Posts: 4
Default How can I tell music has been an MP3? Quantitative Measurement of Fidelity

On Jun 23, 10:18 am, Dave > wrote:
> I have been disappointed with the audio quality of some CDs I have
> bought recently. Is there a free program I can use to get an accepted
> measurement of fidelity? (like a signal to noise ratio)
>
> I have my suspicious that some may have been stored an MP3s and then
> "unripped" in the factory. So how can I tell for certain if my CD has
> been an MP3, or other lossy format? I'd hope mp3 storage would leave
> different markers than the original tape, for example.
>
> To get a good measure I'd expect some Fourier transforms and signal
> analysis to be done, so this should be relevant to sci.physics.


The SNR or more correctly the signal to quantization noise level
depends on the sampler. For N bits it is approx 6N. So for 16 bits it
is 96dB. You will never hear the quantization noise. Compression is a
different matter

  #10  
Old June 23rd 07, 09:32 AM posted to rec.audio.tech,uk.rec.audio,rec.audio.pro,sci.physics
Dave
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Posts: 8
Default How can I tell music has been an MP3? Quantitative Measurement of Fidelity

On 23 Jun, 03:43, "Richard Crowley" > wrote:
> "Dave" wrote ...
>
> > , "Richard Crowley" wrote:
> >> 1) SNR is not "an accepted measurement of fidelity"
> >> 2) There is no specific "accepted measurement of fidelity"
> >> "Fidelity" is a combination of many things. Some subjective.
> >> 3) It would be difficult-to-impossible to actually meausre SNR
> >> on a commercial CD because of the way they are mastered.
> >> (i.e. there is no "baseline" because it is usually muted)

> > Have there been no bright PhD students sponsored by the music
> > industry, or are they too busy with their revenue stream? The noise
> > is what is not the notes. For a symphony you have an idea of what the
> > notes should be, because you have the sheet music, and you know what a
> > violin, flute etc should sound like. You may be able to measure
> > something more because that is what the brain does.

>
> That is just impossibly simplistic. There is a great deal of stuff
> "between the notes" besides noise. Have you done much
> recording yourself?

It doesn't sound as complicated as fusion, and that is having billions
spent on it. Besides I thought banks and defence liked graduates with
in-depth signal analysis experience.

I have listened to plenty of CD (about 650), so I think I can tell a
good recording from a bad one. There may be problems of course with
quantative measurement, in that the recording could be done to get the
measurement
high, and it could just sound clinical.

The point was that if I thought a CD sounded poor quality I think
there should be a computer program to confirm this, instead of just
asking someone else.

 




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