Re: [linux-audio-dev] Random thought on HDR latency compensation

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Subject: Re: [linux-audio-dev] Random thought on HDR latency compensation
From: Paul Barton-Davis (pbd_AT_Op.Net)
Date: Thu Apr 20 2000 - 19:33:53 EEST


In message <38FE93AD.F8D951E_AT_yahoo.com>you write:
>Tom Pincince wrote:
>> Musicians don't monitor from the playback head but recording engineers
>> do. This is called confidence monitoring, because the recording
>> engineer can be confident that what he hears is exactly what has been
>
>This is a good point. Paul, how hard would it be for ardour to give
>an option to monitor tracks "post-record"? Does that add yet another
>layer of buffering headaches? Especially since you'd have to be
>able to do this _simultaneously_ with monitoring "pre-tape"? It
>would be nice if ardour could send at least one or two separate
>outputs that could be patched to "post-tape" monitoring for the
>engineer...

There are a number of options here.

1) If you use a Hammerfall, you can push the "H/W Monitor" button in
   ardour, and all monitoring will be done by the Hammerfall directly
   routing the input data stream to the output data port with 1 sample
   latency. There is no s/w involvement.

2) At the present time, monitoring for tracks that are record-enabled
   is done using the h/w thru facility of the Hammerfall for those
   particular tracks. This corresponds to monitoring "pre-tape".

3) Monitoring for tracks that are not record-enabled is obviously done
   using the data stored on disk. Right now, there is no plugin
   support in ardour, so the data that goes into the output stream is
   identical to whats on the disk.

4) It would be easy, and computationally cheap, to have ardour do
   record-monitoring by copying the data from the input stream to the
   output stream rather than use a h/w facility like the one on the
   Hammerfall. This will obviously be necessary with other cards.

   However, even this is not really "post-record" in the same sense as
   on a tape recorder, since that actually reads the data back from
   the tape. But, as Jörn pointed out, this doesn't make as much
   sense with HDR, because we really don't expect any data loss or
   track slippage or motor jitter at all. Essentially, whatever comes
   in via the audio interface h/w is what ends up on disk.

5) If ardour was to start supporting plugins at record time, then it
   would make sense to drop the use of the h/w monitor facility, and
   have it copy data to the output stream *after* plugin processing
   has happened. This would be about as a close to "post-record" as I'd
   want to get. Re-reading the data from the disk would up the
   necessary data rates to an almost impossible level for anyone with
   a disk more than 1 year old.

If anyone has other ideas, please let me know.

--p


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