Re: iMac input offset ?
Re: iMac input offset ?
- Subject: Re: iMac input offset ?
- From: Shaun Wexler <email@hidden>
- Date: Fri, 6 Jun 2003 19:02:09 -0700
On Friday, June 6, 2003, at 12:47 PM, Brian Willoughby wrote:
[ That is a fluke that I've also seen in Titanium G4 PowerBooks (a 400
[ and an 800, specifically). There is a one sample offset between
left
[ and right input channels, which also includes the built-in line
input.
[ --
[ Shaun Wexler
Hmm, I thought Jean was referring to a DC offset. Either way, I would
be
curious to know the details.
I have seen a left:right sample offset with certain devices connected
via
S/PDIF, which may depend upon the driver and OS (I compared the same
digital
I/O hardware on Mac OS 9 and X).
How are you determining the sample offset?
Cross-correlation, as well as relative phase of the transfer function.
MacFOH provides a suite of multichannel digital audio analyzers as one
of its three major features.
My clue was that transitions (on tape) from silence to signal would
start one
sample early in one channel. I was trying to edit out the silence at
the
beginning and end of a capture from DAT to computer over S/PDIF, and
was
surprised to see an uneven transition. Of course, I have no way of
knowing
whether this is normal for DAT with a flying erase head, an error in
my deck,
or an error in the S/PDIF driver. I did seem to think that
play-through on the
digital I/O device had left & right swapped, but recording into the
computer
and then playing back seemed to preserve the image.
Sorry for rambling, I just want to find out what you're each talking
about.
Should I file a bug? At first, I thought it might be futile to file a
bug against the hardware, and/or it would have already been a known
issue, but it could also be a bug in the AppleDBDMAAudio driver. The
HAL also reports the latency as 32 samples for input and 31 samples for
output, whereas on my non-laptop systems, they are both reported as 32
samples. Curious...
--
Shaun Wexler
MacFOH
http://www.macfoh.com
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