[Legaldeejay]

I've always wanted to know whether there is any true quality loss in the
following circumstances:

1. I burn a 192 kbps mp3 file to CD as a .wav file so that it can play on
a CD player. If I re-create an mp3 file at 192 kbps from that same CD, is
there any quality loss?

2. I open a 192 kbps mp3 file in Soundforge to edit. Soundforge creates a
temporary file for editing. Once I edit the file, I save the new file as a
a 192 kbps mp3 file. Is there any quality loss in this process?

3. I run a 192 kbps mp3 file through a normalizing program like Mptrim. If
the program makes changes to the file, such as eliminating silence at the
beginning of the file and normalizing the volume, is there any quality loss?

Thanks

[Don Pearce]

Legaldeejay wrote:
I've always wanted to know whether there is any true quality loss in the
following circumstances:

1. I burn a 192 kbps mp3 file to CD as a .wav file so that it can play on
a CD player. If I re-create an mp3 file at 192 kbps from that same CD, is
there any quality loss?

Yes

2. I open a 192 kbps mp3 file in Soundforge to edit. Soundforge creates a
temporary file for editing. Once I edit the file, I save the new file as a
a 192 kbps mp3 file. Is there any quality loss in this process?

Yes


3. I run a 192 kbps mp3 file through a normalizing program like Mptrim. If
the program makes changes to the file, such as eliminating silence at the
beginning of the file and normalizing the volume, is there any quality loss?

Yes

Use MP3 as nothing but a final product, and even then always keep an
uncompressed .wav file for future use.

d

[Legaldeejay]

But in situation 2, I know there may be a quality loss when creating the
Mp3, but how about when editing the Mp3? Programs like Soundforge and
CoolEdit will create a temporary file to edit, and once you are done, you
save the new .mp3 file. Are you saying no quality loss at all when creating
a new .mp3 file from a previous .mp3 file?

I also just thought of another situation: When zipping and unzipping mp3
files in Winzip and WinRar, is there any quality loss? I have read that it
is lossless. Do you agree?

Thanks.

"Don Pearce" wrote in message
et...
Legaldeejay wrote:
I've always wanted to know whether there is any true quality loss in the
following circumstances:

1. I burn a 192 kbps mp3 file to CD as a .wav file so that it can play
on
a CD player. If I re-create an mp3 file at 192 kbps from that same CD,
is
there any quality loss?

Yes

2. I open a 192 kbps mp3 file in Soundforge to edit. Soundforge
creates a
temporary file for editing. Once I edit the file, I save the new file as
a
a 192 kbps mp3 file. Is there any quality loss in this process?

Yes


3. I run a 192 kbps mp3 file through a normalizing program like Mptrim.
If
the program makes changes to the file, such as eliminating silence at the
beginning of the file and normalizing the volume, is there any quality
loss?

Yes

Use MP3 as nothing but a final product, and even then always keep an
uncompressed .wav file for future use.

d

[William Sommerwerck]

Briefly...

I've always found this a bit strange, as reconverting a file made at a
particular bitrate with a particular coder, using the same rate and code
(note what I said), should show little or no loss, because the damage has
already been done.

In other words, if the coder has initially "ignored" (and therefore not
coded) certain elements in the original, why should it start attacking the
remaining elements on the second coding cycle? I had assumed that such
psychoacoustic judgements were absolute, not relative.

[Don Pearce]

Legaldeejay wrote:
But in situation 2, I know there may be a quality loss when creating the
Mp3, but how about when editing the Mp3? Programs like Soundforge and
CoolEdit will create a temporary file to edit, and once you are done, you
save the new .mp3 file. Are you saying no quality loss at all when creating
a new .mp3 file from a previous .mp3 file?


Every time you save even a minor edit, the file is re-encoded, further
compromising the quality. That is why when you may be creating multiple
generations it is imperative that you save in a lossless manner, like
..wav. If you are really stuck for space (and who is these days?), use
lossless compression like flac.

I also just thought of another situation: When zipping and unzipping mp3
files in Winzip and WinRar, is there any quality loss? I have read that it
is lossless. Do you agree?


That is entirely lossless. Those compression systems are designed for
bit-perfect recovery. They are also particularly poor at compressing
audio files, since these do not contain the kind of patterns they rely on.

d

[Anahata]

On Wed, 27 Aug 2008 07:14:28 -0400, Legaldeejay wrote:

3. I run a 192 kbps mp3 file through a normalizing program like Mptrim.
If the program makes changes to the file, such as eliminating silence
at the beginning of the file and normalizing the volume, is there any
quality loss?

Certain operations can be carried out on an MP3 without loss of quality.
Cutting off tops and tails is one of those operations, and the other is
"scaling" where the volume level of the whole file can be adjusted but
only in fairly coarse steps.

I don't know Mptrim but there's a chance it can do this.

Cases 1 and 2 always involve quality loss, and please heed all the other
advice that you should process and archive everything in linear PCM
format e.g. .WAV files (disk space is cheap enough now...) and only use
MP3 for final distribution/playback, if it's needed in that format.

--
Anahata
==//== 01638 720444
http://www.treewind.co.uk ==//== http://www.myspace.com/maryanahata

[John O[_2_]]

"Legaldeejay" wrote in message
...
But in situation 2, I know there may be a quality loss when creating the
Mp3, but how about when editing the Mp3? Programs like Soundforge and
CoolEdit will create a temporary file to edit, and once you are done, you
save the new .mp3 file. Are you saying no quality loss at all when
creating
a new .mp3 file from a previous .mp3 file?

I also just thought of another situation: When zipping and unzipping mp3
files in Winzip and WinRar, is there any quality loss? I have read that
it
is lossless. Do you agree?

WinZip uses a compression system that ensures not a single bit is
lost...uncompressing generates the *exact* same file you started with. It's
lossless.

mp3 is like jpg...in order to achieve compression the system throws out data
it feels is unnecessary. Uncompressing DOES NOT give you the same thing you
started with. It's lossy.

Think of mp3 (and jpg) as a VHS copy. Each time you open and resave as mp3,
you make another generation of that tape. It eventually gets so bad there's
nothing left. The first couple generations might not be too bad, but after
that....

Also, the highest bitrates throw away less of the original data. This is
true of all lossy compression schemes with variable compression settings. If
your mp3s are higher than 192 you have more room for subsequent generations
before the loss gets unbearable. But that's all relative.

As Don said....mp3 is a final format, not an intermediate step--if you have
any sense of or need for audio quality.

-John O

[Mike Rivers]

Legaldeejay wrote:

1. I burn a 192 kbps mp3 file to CD as a .wav file so that it can play on
a CD player. If I re-create an mp3 file at 192 kbps from that same CD, is
there any quality loss?

Why not try it and listen for yourself? Or are you concerned that there
will be a loss that you can't here but someone else will, and then
you'll be subject to great mockery and derision? Why are you worried
about quality loss of an MP3 file anyway? Nearly all the damage that can
be done has already been done by the data thrown away by the data
reduction process of creating the MP3.

Now if you were to ask if you got an identical file back from the CD, I
suspect not, in fact I'm quite sure of it. But this is easy enough to
verify with the computer doing all the work - no ears required.

2. I open a 192 kbps mp3 file in Soundforge to edit. Soundforge creates a
temporary file for editing. Once I edit the file, I save the new file as a
a 192 kbps mp3 file. Is there any quality loss in this process?

Probably none that you'd notice, but again, listen and tell us what YOU
think.

3. I run a 192 kbps mp3 file through a normalizing program like Mptrim. If
the program makes changes to the file, such as eliminating silence at the
beginning of the file and normalizing the volume, is there any quality loss?

Absolutely. But then you might gain overall "listenability" because it's
louder and has less uninteresting junk in it.

If you're really worried about quality, work with WAV files and make the
conversion to MP3 as the final step. Then you'll be assured a loss of
quality, but only one time.

--
If you e-mail me and it bounces, use your secret decoder ring and reach
me he
double-m-eleven-double-zero at yahoo -- I'm really Mike Rivers
)

[Mike Rivers]

Legaldeejay wrote:

I know there may be a quality loss when creating the
Mp3, but how about when editing the Mp3? Programs like Soundforge and
CoolEdit will create a temporary file to edit, and once you are done, you
save the new .mp3 file.

You don't simply "save" a new MP3 file, you convert the temporary PCM
file (probably WAV) to MP3. Every time you do that, there's some data
thrown away, so there will be some loss of quality. But you're probably
not talking about a severe enough loss to worry about. It's not like you
were converting it to 32 kbps or reducing the PCM file to 8 bits or 11
kHz sample rate.

I also just thought of another situation: When zipping and unzipping mp3
files in Winzip and WinRar, is there any quality loss? I have read that it
is lossless. Do you agree?

ZIP is a lossless data compression process, so it's completely
reversible without data loss. Unlike MP3, which throws away data that
the program doesn't think you can hear, ZIP only looks for repeated data
and writes a shorthand representation of it. I don't know how much data
compression you get when ZIPping an MP3 file, but you don't save too
much by space ZIPping a WAV file.


--
If you e-mail me and it bounces, use your secret decoder ring and reach
me he
double-m-eleven-double-zero at yahoo -- I'm really Mike Rivers
)

[Scott Dorsey]

Legaldeejay wrote:
I've always wanted to know whether there is any true quality loss in the
following circumstances:

1. I burn a 192 kbps mp3 file to CD as a .wav file so that it can play on
a CD player. If I re-create an mp3 file at 192 kbps from that same CD, is
there any quality loss?

Yes. Re-encoding is always a bad thing to do, and some arguments have been
made that successive re-encoding steps are worse sonically than the first
one. Skip Pizzi did a lot of experiments back when perceptual encoding systems
were new, though i don't know how well his tests apply to more modern
encoders.

2. I open a 192 kbps mp3 file in Soundforge to edit. Soundforge creates a
temporary file for editing. Once I edit the file, I save the new file as a
a 192 kbps mp3 file. Is there any quality loss in this process?

Yes, for the same reason.

3. I run a 192 kbps mp3 file through a normalizing program like Mptrim. If
the program makes changes to the file, such as eliminating silence at the
beginning of the file and normalizing the volume, is there any quality loss?

If Mptrim is what I think it is, the answer is no, because it does not
decode and re-encode the file. The problem with editing Mp3s without
decoding them is that you can only cut on a block boundary, which limits
your possible edit points. You can't normalize very effectively either,
you can just change the gain at which it's played back.

For the most part, perceptually encoded files are not acceptable for
production work. Create a normal, unencoded file, keep all your work
files unencoded, and only compress down to mp3 for the actual release.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

William Sommerwerck wrote:

I've always found this a bit strange, as reconverting a file made at a
particular bitrate with a particular coder, using the same rate and code
(note what I said), should show little or no loss, because the damage has
already been done.

It doesn't.

In other words, if the coder has initially "ignored" (and therefore not
coded) certain elements in the original, why should it start attacking the
remaining elements on the second coding cycle? I had assumed that such
psychoacoustic judgements were absolute, not relative.

It doesn't. And what is REALLY interesting is that making an analogue dub
between two machines using perceptual encoding systems can actually sound
BETTER than a digital one, because of the slight level changes involved.

Look up some of Skip Pizzi's tests. He had a couple AES conference papers,
and a bunch of articles in Radio World in the early nineties.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[jwvm]

On Aug 27, 7:22*am, Don Pearce wrote:
snip

3. *I run a 192 kbps mp3 file through a normalizing program like Mptrim. *If
the program makes changes to the file, such as eliminating silence at the
beginning of the file and normalizing the volume, is there any quality loss?

Yes

Use MP3 as nothing but a final product, and even then always keep an
uncompressed .wav file for future use.

d

Actually, there are programs that claim to change mp3 volume
losslessly. The spectral magnitudes can be scaled without fully
decoding and re-encoding the signal.

[Scott Dorsey]

jwvm wrote:

Actually, there are programs that claim to change mp3 volume
losslessly. The spectral magnitudes can be scaled without fully
decoding and re-encoding the signal.

Right. ALL you can do is fixed gain adjustment, and editing on block
boundaries, but this is really quite enough for rough assembly work.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Les Cargill]

Legaldeejay wrote:
I've always wanted to know whether there is any true quality loss in the
following circumstances:

1. I burn a 192 kbps mp3 file to CD as a .wav file so that it can play on
a CD player. If I re-create an mp3 file at 192 kbps from that same CD, is
there any quality loss?


It would depend on the encode and decode of the .mp3. I have done round
trips with LAME at -V 1 (highest rate VBR ) and there's no
loss the second time. IOW, for my tests, LAME has
proven to be deterministic.

I only did this because a remote client wanted delivery in .mp3
rather than waiting for a CD.

2. I open a 192 kbps mp3 file in Soundforge to edit. Soundforge creates a
temporary file for editing. Once I edit the file, I save the new file as a
a 192 kbps mp3 file. Is there any quality loss in this process?


Try it. Add a slate mark ( a single sample pulse) to a full-rate .wav,
encode, realign and subtract the two vectors. Decode, repeat, lather,
rinse.

3. I run a 192 kbps mp3 file through a normalizing program like Mptrim. If
the program makes changes to the file, such as eliminating silence at the
beginning of the file and normalizing the volume, is there any quality loss?


No idea.

In general, only encode once. Then there's no problem.

Thanks



--
Les Cargill

[Les Cargill]

William Sommerwerck wrote:
Briefly...

I've always found this a bit strange, as reconverting a file made at a
particular bitrate with a particular coder, using the same rate and code
(note what I said), should show little or no loss, because the damage has
already been done.

In other words, if the coder has initially "ignored" (and therefore not
coded) certain elements in the original, why should it start attacking the
remaining elements on the second coding cycle? I had assumed that such
psychoacoustic judgements were absolute, not relative.




The question becomes "over what domain of settings is a given encoder
deterministic", and the answer is "it depends." For VBR -V 1, LAME
appears to be - for a very small sample set.

--
Les Cargill