Subject: [linux-audio-user] Mastering; Rezound, fir filter, digital clipping
From: R Parker (rtp405_AT_yahoo.com)
Date: Fri Jun 13 2003 - 20:05:32 EEST
Hi,
I'm doing a study on audio mastering. Hopefully this
letter will generate some correspondance from which
I'll learn enough to augment a GFDL licensed document
that I've been working on.
The test job is an album I recorded several years ago.
The source I've decided to use is 16bit 44100 audio
CD. I'm restricting the applications I use to jack
clients.
I guess the process of copying audio and data from CD
doesn't introduce any opportunity to compromise the
sonic quality of the source. Am I right or wrong?
Having opened the songs in Rezound, I've discovered
that some of the songs have an inordinate amount of
clipping--represented by vertical red lines on the
time line. For the purposes of testing this is
excellent because they're an opportunity to solve a
common problem. The clips cause a series of questions
for which I absolutely do not have definitive answers.
Is what I am seeing clipping or is there a more
accurate term to describe what I'm seeing?
Perhaps someone could provide a technical explanation
of clipping or a link to a definition.
What tools do you use for eliminating clipping that
already exists in a source? I don't care at all about
preventing the problem.
For the moment I am using the Rezound Arbitrary Fir
Filter to identify the hz where the clips occur and am
performing a decibal cut on the problem range. The
interface for this filter enabled me to do some
detailed work. Reguardless of how detailed I get,
there's an audible consequence to eliminating the
clips.
I configured a preset with the minimal settings
required to eliminate the clips but the result is
audibly unacceptable. Another preset eliminates about
80% of the clips and audibly is marginally acceptable
if applied to the entire file.
What's interesting about this specific set of clips is
that they are mostly inaudible. The clipping occurs
around 10kHz -> 15kHz and are almost all within the
high hat.
This causes me to wonder:
*how Rezound is configured to conclude that there are
clips
*should measuring for these types of problems be user
configurable or does a technical specification define
when a clip occurs
*can engineers safely ignore inaudible clips and tell
their clients that there's room to fudge and not to
worry
Is a Fir filter a good tool for addressing the problem
of digital clips or is there something better?
Are there alternative Fir filter algorithms that
produce better results than the one being used in
Rezound? I haven't a clue what Rezound uses.
Anyway, there's a few of my questions which I realize
are probably enough to exhaust anyone's patience.
Reguardless, I really would appreciate your thoughts.
ron
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