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From: Jos Geluk on 6 May 2008 16:37
Dennis Q. Wilson schreef:
> Is there any software to tell whether an audio track was actually
> converted from an MP3 or WMA file, rather than ripped from a CD?

To add to the others' good advice, here is one trick. In the audio
application of your choice, open the track, then flip the left and right
channels, then invert the phase. Then play this together with the
original track. If the original track has been compressed to a low bit
rate somewhere along the way, you will hear artifacts all over the place.

HTH

Jos.

--
Ardis Park Music
www.ardispark.nl
From: Mark on 6 May 2008 17:05
On May 6, 4:23 pm, nos...(a)nospam.com (Don Pearce) wrote:
> On Tue, 6 May 2008 11:24:32 -0700 (PDT), "Dennis Q. Wilson"
>
> <DennisQWil...(a)yahoo.com> wrote:
> >Is there any software to tell whether an audio track was actually
> >converted from an MP3 or WMA file, rather than ripped from a CD?
>
> Have a look at this:
>
> http://81.174.169.10/odds/identmp3.gif
>
> It is the spectrogram of a few seconds of music on a CD, followed by
> the same piece following 256k conversion to MP3. The differences are
> obvious, the main one being the complete lack of low level detail
> above 16kHz - only the peaks are showing. Apart from that, the whole
> appearance of the MP3 section is more granular which is evidence of
> the amount of data you can discard because it is masked. Audibly, the
> two pieces are essentially identical.
>
> The piece I have used is opera with virtually no amplitude compression
> - that being the kind of stuff that MP3 does best; it really doesn't
> like having to cope with hypercompressed pop music that doesn't
> contain the kind of low level detail that can be masked away.
>
> Anyway, what this shows is that visually it is very easy to tell a
> file that has been through MP3 conversion from one that hasn't.
>
> d
>
> --
> Pearce Consultinghttp://www.pearce.uk.com

hey look at that!

the MP3 got rid of all the hiss :-)

Mark
From: Dennis Q. Wilson on 6 May 2008 17:17
On May 6, 11:24 am, "Dennis Q. Wilson" <DennisQWil...(a)yahoo.com>
wrote:
> Is there any software to tell whether an audio track was actually
> converted from an MP3 or WMA file, rather than ripped from a CD?

Thank you, one and all. I have come away from this exchange with a
lot of solid, practical information.
From: Arny Krueger on 7 May 2008 10:06
"Mark" <makolber(a)yahoo.com> wrote in message
news:a16a362d-649f-41c4-92fd-b43296cb0fea(a)z72g2000hsb.googlegroups.com
> On May 6, 4:23 pm, nos...(a)nospam.com (Don Pearce) wrote:
>> On Tue, 6 May 2008 11:24:32 -0700 (PDT), "Dennis Q.
>> Wilson"
>>
>> <DennisQWil...(a)yahoo.com> wrote:
>>> Is there any software to tell whether an audio track
>>> was actually converted from an MP3 or WMA file, rather
>>> than ripped from a CD?
>>
>> Have a look at this:
>>
>> http://81.174.169.10/odds/identmp3.gif
>>
>> It is the spectrogram of a few seconds of music on a CD,
>> followed by the same piece following 256k conversion to
>> MP3. The differences are obvious, the main one being the
>> complete lack of low level detail above 16kHz - only the
>> peaks are showing.

Agreed and expected.


>> Apart from that, the whole appearance
>> of the MP3 section is more granular which is evidence of
>> the amount of data you can discard because it is masked.

I don't see that at all. What I see is the usual granular nature of a
spectrogram with the parameters used.

>> Audibly, the two pieces are essentially identical.

>> The piece I have used is opera with virtually no
>> amplitude compression - that being the kind of stuff
>> that MP3 does best; it really doesn't like having to
>> cope with hypercompressed pop music that doesn't contain
>> the kind of low level detail that can be masked away.

>> Anyway, what this shows is that visually it is very easy
>> to tell a file that has been through MP3 conversion from
>> one that hasn't.

> hey look at that!

> the MP3 got rid of all the hiss :-)

I wish.

Audible hiss is usually above -60 dB, and down in the 4 KHz range where the
ear is most sensitive.

IME, a 256K MP3 pretty well preserves low level detail down into the -60 dB
range, so its not going to remove audible hiss, and its not going to producw
a spectrogram with appreciable visible changes due to the removal of
low-level detail.


From: Art Cohen on 7 May 2008 12:28
> In article <c46b389d-d52e-418b-969c-3548a509b226(a)z24g2000prf.googlegroups.com>,
> Dennis Q. Wilson <DennisQWilson(a)yahoo.com> wrote:
> >Is there any software to tell whether an audio track was actually
> >converted from an MP3 or WMA file, rather than ripped from a CD?
>
<snip>
There are several software apps that purport to do exactly that.
"Trader's Little Helper" is one. I'm guessing that they work by looking
for the same characteristics mentioned elsewhere in this thread. This is
a big deal in the lossless live music trading community, where polluting
the dataspace with lossy compressed sources is strictly verboten.

Peace
Art
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