Question about audio artifacts: WMA vs. MP3

[Radium[_4_]]

Hi:

Why is it that MP3s needs some amount of encoded audio in order to
have any audio at all, while WMA can simply make its own audio? [To
better understand this question, read below]

I have Adobe Audition 1.5 in which I do audio experiments.

Below is my first experiment:

1. I make a silent 44.1 KHz-sample-rate, 16-bit-resolution, monaural
wave file that is 4 seconds long. [To do this, go to "generate" and in
the drop-down menu click "silence". A small windows pops up giving the
number of seconds, I put it at '4']

2. I save it as "silent.wav."

3. I then convert this wave file to a 44.1-KHz-sample-rate, monaural,
20kbps WMA file -- "silent.wma."

4. I close silent.wma

5. I open silent.wma and convert it to a 44.1 KHz-sample-rate, 16-bit-
resolution, monaural wave file and save it as "silent.wav" again --
this overwrites the original "silent.wav."

6. I then close silent.wav and then re-open it. Then I convert it back
to 44.1-KHz-sample-rate, monaural, 20kbps "silent.wma" file
[overwriting the original "silent.wma"].

After generating the silent.wav file I repeat steps 2-6 at least 4
times. Now when I play silent.wma I notice audio in the file that
resembles the characteristic artifacts of WMA.

In my second experiment, I do the exact same thing, except I use MP3
instead of WMA:

1. I make a silent 44.1 KHz-sample-rate, 16-bit-resolution, monaural
wave file that is 4 seconds long. [To do this, go to "generate" and in
the drop-down menu click "silence". A small windows pops up giving the
number of seconds, I put it at '4']

2. I save it as "silent2.wav."

3. I then convert this wave file to a 44.1-KHz-sample-rate, monaural,
32kbps MP3 file -- "silent2.mp3."

4. I close silent2.mp3

5. I open silent2.mp3 and convert it to a 44.1 KHz-sample-rate, 16-bit-
resolution, monaural wave file and save it as "silent2.wav" again --
this overwrites the original "silent2.wav."

6. I then close silent2.wav and then re-open it. Then I convert it
back to 44.1-KHz-sample-rate, monaural, 32kbps "silent2.mp3" file
[overwriting the original "silent2.mp3"].

After generating the silent2.wav file I repeat steps 2-6 more than 4
times. No matter how many times I repeat 2-6, silent2.mp3 still
remains completely silent. Why is this?


Thanks,

Radium

P.S. In my post I am describing lossy WMA compression. The standard
WMA.

[[email protected]]

On Aug 16, 1:51 am, Radium > wrote:
> Hi:
>
> Why is it that MP3s needs some amount of encoded audio in order to
> have any audio at all, while WMA can simply make its own audio? [To
> better understand this question, read below]
> [snip long recipe]

First, your question doesn't quite make sense, given the steps you are
describing. Introduction of audible artifacts counts as "simply make
its own audio?" I don't quite see what you are getting at.

Second, your experiment has too many variables to tell us anything
about which is a better encoder.

Just as an example, you are using Adobe Audition to resample back and
forth between 44.1 KHz and 20 KHz. The code doing this may have
nothing to do with either the MP3 or WAV formats - it could be all
Adobe, and that may be where the artifacts are coming from.

Both the WMA and MP3 codecs have the ability to reproduce pretty
decent audio, and neither will stand up to the standards of an
audiophile. Getting worked up about the differences between them is
probably pointless. This is particularly true as a user of digital
audio. If you are a producer of digital audio or products that use it,
the big question between the two IP-bound products is which big
company you decide you want to pay royalties to (and perhaps whether
you must have DRM.)

|
| Mark Nelson - http://marknelson.us
|

[Ron Capik]

Radium wrote:

> Hi:
>
> Why is it that MP3s needs some amount of encoded audio in order to
> have any audio at all, while WMA can simply make its own audio? [To
> better understand this question, read below]
>
> I have Adobe Audition 1.5 in which I do audio experiments.
> < ...snip... >

It would seem you have a poorly designed experiment
I believe you should rethink your thesis and create
experiments to explore that thesis.
Use the data from the experiments to tweak the thesis
and devise new experiments.


Later...

RC
--

[Serge Auckland]

"Radium" > wrote in message
ups.com...
> Hi:
>
> Why is it that MP3s needs some amount of encoded audio in order to
> have any audio at all, while WMA can simply make its own audio? [To
> better understand this question, read below]
>
> I have Adobe Audition 1.5 in which I do audio experiments.
>
> Below is my first experiment:
>
> 1. I make a silent 44.1 KHz-sample-rate, 16-bit-resolution, monaural
> wave file that is 4 seconds long. [To do this, go to "generate" and in
> the drop-down menu click "silence". A small windows pops up giving the
> number of seconds, I put it at '4']
>
> 2. I save it as "silent.wav."
>
> 3. I then convert this wave file to a 44.1-KHz-sample-rate, monaural,
> 20kbps WMA file -- "silent.wma."
>
> 4. I close silent.wma
>
> 5. I open silent.wma and convert it to a 44.1 KHz-sample-rate, 16-bit-
> resolution, monaural wave file and save it as "silent.wav" again --
> this overwrites the original "silent.wav."
>
> 6. I then close silent.wav and then re-open it. Then I convert it back
> to 44.1-KHz-sample-rate, monaural, 20kbps "silent.wma" file
> [overwriting the original "silent.wma"].
>
> After generating the silent.wav file I repeat steps 2-6 at least 4
> times. Now when I play silent.wma I notice audio in the file that
> resembles the characteristic artifacts of WMA.
>
> In my second experiment, I do the exact same thing, except I use MP3
> instead of WMA:
>
> 1. I make a silent 44.1 KHz-sample-rate, 16-bit-resolution, monaural
> wave file that is 4 seconds long. [To do this, go to "generate" and in
> the drop-down menu click "silence". A small windows pops up giving the
> number of seconds, I put it at '4']
>
> 2. I save it as "silent2.wav."
>
> 3. I then convert this wave file to a 44.1-KHz-sample-rate, monaural,
> 32kbps MP3 file -- "silent2.mp3."
>
> 4. I close silent2.mp3
>
> 5. I open silent2.mp3 and convert it to a 44.1 KHz-sample-rate, 16-bit-
> resolution, monaural wave file and save it as "silent2.wav" again --
> this overwrites the original "silent2.wav."
>
> 6. I then close silent2.wav and then re-open it. Then I convert it
> back to 44.1-KHz-sample-rate, monaural, 32kbps "silent2.mp3" file
> [overwriting the original "silent2.mp3"].
>
> After generating the silent2.wav file I repeat steps 2-6 more than 4
> times. No matter how many times I repeat 2-6, silent2.mp3 still
> remains completely silent. Why is this?
>
>
> Thanks,
>
> Radium
>
> P.S. In my post I am describing lossy WMA compression. The standard
> WMA.
>

MP3 is a perceptual encoder, that means that within the many narrow filter
bands, sounds that are masked by other sounds are not encoded.

I may be wrong on this, but I don't think WMA is a perceptual encoder. If
so, multiple encode/decode cycles will add low-level artefacts which with
repeated code/decode cycles will become very audible. MP3, being a
perceptual encoder, will encode silence "perfectly", and decode it equally
perfectly, so artefacts won't be created. Try the same experiment with some
audio, and you will see (hear?) MP3 artefacts adding. If you take some
audio, encode MP3, decode, then encode MP2 then decode, then encode MP3 (or
alternatively encode/decode MP3 with different bit rates) you will hear the
artefacts easily. In other words, MP3 creates artefacts on audio, but only
when there is some audio to create them on. It is the reason why in the UK
radio stations with a digital output (DAB, DSAT or whatever) do not allow
the use of any data-compressed programme source as multiple encode/decode
cycles are very audible.

S.



--
http://audiopages.googlepages.com

[Radium[_4_]]

On Aug 16, 5:52 am, " > wrote:

> First, your question doesn't quite make sense, given the steps you are
> describing.

Why not?

> Introduction of audible artifacts counts as "simply make
> its own audio?"

Yes. It seems like WMA can recognize even the smallest amount of EMI/
RFI and encode it. MP3, OTOH, needs sounds to be louder in order for
it to recognize it.

Just because the file contains 'silence' does not prevent extremely
extremely weak wattage of electrical disturbances from showing up in
the audio file. At some level there is always some amount of EMI/RFI.

>From what I guess, WMA has the ability to encode such small voltages
[resulting from minute electrical disturbances] while MP3 doesn't.
This is probably because of the way the WMA compression scheme is
designed vs. the compression scheme of MP3.

I could be so wrong though.

> Second, your experiment has too many variables to tell us anything
> about which is a better encoder.

Like what?

> Just as an example, you are using Adobe Audition to resample back and
> forth between 44.1 KHz and 20 KHz. The code doing this may have
> nothing to do with either the MP3 or WAV formats - it could be all
> Adobe, and that may be where the artifacts are coming from.

Nope. I've done the same experiment with audio applications other than
Adobe Audition -- e.g. Wavelab. Adobe has little -- if anything -- to
do with it. AFAIK, it's got most to do with MP3/WMA compressions
themselves.

> Both the WMA and MP3 codecs have the ability to reproduce pretty
> decent audio, and neither will stand up to the standards of an
> audiophile. Getting worked up about the differences between them is
> probably pointless.

I am not getting worked-up. I am simply interested. However, I am
getting a bit frustrated now as this seems like a question that cannot
be answered. If it can't be answered, I am going to get furious.

[Radium[_4_]]

On Aug 16, 5:52 am, " > wrote:

> resample back and
> forth between 44.1 KHz and 20 KHz.

Huh? I never changed the sample rate. The *sample*-rate always 44.1
KHz. The *bit*-rate is 20 kbps.

There is a huge difference between *bit*-rate and *sample*-rate. They
are two totally different things please don't confuse them.

I really frustrates me when *bit*-rate and *sample*-rate are thought
of as the same thing.

[Geoff]

Radium wrote:
> On Aug 16, 5:52 am, " > wrote:
>
>> resample back and
>> forth between 44.1 KHz and 20 KHz.
>
> Huh? I never changed the sample rate. The *sample*-rate always 44.1
> KHz. The *bit*-rate is 20 kbps.
>
> There is a huge difference between *bit*-rate and *sample*-rate. They
> are two totally different things please don't confuse them.
>
> I really frustrates me when *bit*-rate and *sample*-rate are thought
> of as the same thing.

Guess what really frustrates everybody else...


geoff

[isw]

In article om>,
" > wrote:

--snip--

> Both the WMA and MP3 codecs have the ability to reproduce pretty
> decent audio, and neither will stand up to the standards of an
> audiophile

Especially if the audiophile knows he's listening to an mp3; it's
considerably less likely he'll notice if he does not...

Isaac

[Thomas Richter]

Radium schrieb:

> Just because the file contains 'silence' does not prevent extremely
> extremely weak wattage of electrical disturbances from showing up in
> the audio file. At some level there is always some amount of EMI/RFI.

Huh? You must be kidding. We are talking about digital files. If the
file is silent, then it is just all-zero. There is no "electrical
disturbance" whatsoever.

So long,
Thomas

[Radium[_4_]]

On Aug 16, 11:39 pm, Thomas Richter > wrote:

> Radium schrieb:

> > Just because the file contains 'silence' does not prevent extremely
> > extremely weak wattage of electrical disturbances from showing up in
> > the audio file. At some level there is always some amount of EMI/RFI.

> Huh? You must be kidding. We are talking about digital files. If the
> file is silent, then it is just all-zero. There is no "electrical
> disturbance" whatsoever.

Okay. Sorry. Electrical interference [an analog entity] is now ruled
out.

So just what gives WMA the ability to produce its own audio - in the
manner which I described in the 1st post of this thread?

[Mr.T]

"Radium" > wrote in message
ups.com...
> On Aug 16, 5:52 am, " > wrote:
>
> > resample back and
> > forth between 44.1 KHz and 20 KHz.
>
> Huh? I never changed the sample rate. The *sample*-rate always 44.1
> KHz. The *bit*-rate is 20 kbps.

Pretty LOW bit rate you use, standard CD's being 70 times higher than that.

> There is a huge difference between *bit*-rate and *sample*-rate. They
> are two totally different things please don't confuse them.
>
> I really frustrates me when *bit*-rate and *sample*-rate are thought
> of as the same thing.

And also when someone can't even spot that 20kHz is neither.

MrT.