14 May
2005
14 May
'05
8:56 a.m.
On Sat, May 14, 2005 at 11:58:45AM +0200, Benno Senoner wrote:
Since we cannot increase the speed at which the sound
travels and even
DACs add some latency (1msec or so)
I see any effort to reduce latency below 2-3msec quite useless.
We know that halving the number of frames (soundcard period size) we run
the audio software at is doubling the IRQ rate
and you can quickly achieve a point where a significative chunk of CPU
is burnt in the IRQ handlers.
It could change if CPU get considerably faster but then you begin to hit
other limits, eg
the PCI DMA minimum transfer sizes which limits your minimum soundcard
period size.
Plus what happens if your speakers are 1m away from the listener ?
Another 3msecs added to the total
"latency between hitting a key and hearing the sound".
If you move the speakers another 50cm away from the ear ? Another
1.5msecs delay get added.
This message came in while I was playing my new piano samples with
Linuxsampler (thanks Benno !). Jackd set to 2 * 256, that's 5.3ms,
about 0.6ms of DAC delay, let's say 1.0ms for midi and 3ms for speaker
to ear distance. That adds up to 9.9ms. Now the piano _is_ a percussive
instrument, the things I was playing were fast enough for my fingers,
and yet I had _no problem at all_ with this delay.
Now I've had some training as an organist, and then you learn to adapt
to much longer latencies - 30ms is quite normal. But I don't think that
is the determining factor.
Humans are more sensitive to differences than to
absolute values.
Right. And every musician (hopefully) learns sooner or later to play
along with others, and that also involves latencies. You just learn
to anticipate.
Eg in physics you feel the acceleration but not the
speed.
That's because you feel force, and we have F = m * a.
Of course some instrument players, especially those
that play percussive
sounds are more sensitive than
others, but the question is how small is this time ? Is there scientific
data around that can state:
"if latency of the virtual percussion instrument is higher then X then
the instrument is unusable for 30% of professional musicians" ?
Not scientific, but I'd expect the most sensitive players to be those
that play acoustic string instruments. They are very near to the sound
source, and there's virtually nothing between them and the strings.
--
FA