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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