Question about audio artifacts; WMA vs. MP3

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?

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 wattages 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.

Please note that there is a huge difference between *bit*-rate and
*sample*-rate. They are two totally different things. Please don't
confuse them.

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

In no part of my experiment do I ever change the sample rate.

I've done the same experiment with audio applications other than Adobe
Audition -- e.g. Wavelab. The results were the same. Adobe has little
-- if anything -- to do with it. AFAIK, it's got most -- if not
everything -- to do with MP3/WMA compressions themselves.


Thanks,

Radium

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

.

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