In article ,
Legaldeejay wrote:
I've always wanted to know whether there is any true quality loss in the
following circumstances:
That depends on what you mean by "true quality loss".
I'll interpret it as meaning "the sonic content of the output, when
played, is detectably different than the sonic quality of the input."
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. In principle, each pass through a "lossy" encoder such as MP3
will result in some loss of quality... loss of certain frequencies,
and/or increased quantization noise (distortion), etc.
The "burn to CD, rip back from CD" step is lossless (if you have a
decent ripping program and good-quality CD-R blanks), but the
subsequent MP3 encoding step is lossy.
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, almost certainly. 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?
Yup.
4. When zipping and unzipping mp3 files in Winzip and WinRar, is there any
quality loss?
No. The compression logic in those algoriths is lossless - the output
of the decompression process is bit-for-bit identical to what went
in.
For all of the above reasons, if you want to manipulate music (or
other audio) via any sort of editing, and maintain the best quality,
you should keep the music in a lossless representation for as long as
possible... e.g. straight PCM, or a losslessly-compressed format such
as FLAC or ZIP or RAR. Do all of your editing and manipulation in
these domains. Then, at the very end of the process, perform whatever
sort of lossy encoding you may want to use for delivery (e.g. MP3, Ogg
Vorbis, RealAudio, etc.), and keep the losslessly-stored version in
your archives for future use.
--
Dave Platt AE6EO
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http://www.radagast.org/jade-warrior
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