On Thu, 3 Aug 2000, David W. Tamkin wrote:
> If the explanation were that the tracks got out of sync, then the soft parts
> of the redundant stereo input would become louder as they got mixed with
> louder volumes. Moreover, how can the two channels of an S/PDIF signal get
> out of sync like that? Every frame contains the left channel and the right
> channel information that should be played at the same time.
Ah... if the whole thing is softer I would certainly point the finger at
the 'monauralizing' algorithm. I agree with you - if the problem was with
channel sync. then the lows would be higher and the highs lower.
My idea with the SPDIF channels getting out of sync. is before encoding of
after decoding - here the channels can be separate and if they were
buffered separately it is possible (but unlikely) for them to get very
slightly out of sync. However we're talking about a DSP here so unless
it's really screwed up it will be able to get the synchronisation right.
> I> Of course the ATRAC may work differently on each of the two channels for
> I> stereo recording...
>
> If ATRAC is destroying the peaks, why doesn't the same effect show up in
> stereo-mode MD recordings? It has to be something in the algorithm for
> shorting stereo to mono. When I have a .wav file on hard disc with two
> identical channels and I convert it to mono, the amplitudes are preserved.
That was a comment on my idea for testing the channel synchronisation of
the SPDIF data stream really, in that a post-stereo-recording comparison
might not be of any use because the two channels may have got compressed
differently (this shouldn't happen if the DSP is well designed and
the channels are exactly the same though).
I am digging for alternative explanations here... most of what I have
suggested is very unlikely indeed: the most likely cause is almost
definitely the stereo->mono conversion. OK... I'll stop trying to think
of things now.
I would certainly be very interested to find out what algorithm Sony are
using. I plan to do a few quick tests myself (probably tomorrow) using my
MDS-JE520 and (homemade) computer digital out. Unfortunately I have no
way of getting the SPDIF back into the computer again so I'll have to rely
on the MD's level meter. What I'll probably do is feed it with a ~250Hz
tone so the level is stable. If I don't get a horrible headache I will
post the results :)
Jonathan
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