Subject: [linux-audio-dev] stream buffering on EVO & pitchbend .... opinions ?
From: Benno Senoner (sbenno_AT_gardena.net)
Date: Sat Sep 16 2000 - 22:17:30 EEST
Hi,
I'm just working on resampling capabilites for EVO
(it's almost working, will release it in a few days).
I need your thoughts on buffering:
I use 128KB for the initial parts ( 64k samples) = 1.5sec of audio
and 256KB for streaming (holds about 3sec of audio)
I am testing resampling by mapping the pitchbender to a +/-4 octaves
(+/-48 semitones).
These are extreme shifts and at maximum up pitch, (+4 octaves), the
tracks play at 16x speed from disk.
And you can immagine that a disk has it's limits too:
first, with 5-6 tracks playing at 16x speed
(would be the same as 80-100tracks playing at normal speed),
the disk bandwidth is maxed out,
plus a second side effect comes into play:
at 16x speed, the initial buffer holds only 1.5sec/16 = 90msec of audio
while the stream buffer holds only 180msec of audio.
That is way too short for a filesystem to react, thus , filesystem
latency will limit us even before the max disk bandwidth is maxed out.
I think larger buffers does not make sense, since it will limit greatly the
number of loadable samples (since we need to load the beginnings of each
sample).
Assume we limit the pitching up to +12 semitones (1octave).
That means the initial part holds 0.75sec of audio while the streambuffer holds
1.5sec, pretty reasonable and in this case although the number of possible
voices will halve, filesystem latency should not be the limiting factor.
(And as far as I know, the normal pitchbend range (at least on general MIDI is
+2/-2 semitones))
So does the limiting to +12 semitones sound reasonable ?
(from a MIDI instrument POV ?)
If you want more, sorry you have to load the entire sample in RAM because the
disk can't simply keep up.
And that is a problem of all disksamplers. (all = all the other hundred
disksamplers out here :-) )
Downpitching is not a problem since playing tracks at lower speed is not an
issue.
comments and thoughts ?
(PS: but it is too funny making the HD go crazy with the simple movement of
the pitchbender :-) )
Benno.
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