Subject: Re: [linux-audio-dev] XAP: a polemic
From: David Gerard Matthews (dgm4+@pitt.edu)
Date: Sun Dec 15 2002 - 04:25:13 EET
David Olofson wrote:
>On Sunday 15 December 2002 00.32, Paul Davis wrote:
>
>>>> * Is there a good reason to make event system timestamps
>>>> relate to musical time rather than audio time?
>>>>
>>>Again, I would rather let the timestamps deal with audio time.
>>>Hosts which work in bars/beats/frames
>>>should be capable of doing the necessary conversion. Remember,
>>>there
>>>
>>you're ignoring *plugins* that want to work with B|b|t durations.
>>the canonical examples that i've mentioned several times are
>>tempo-synced LFO's and delays. these can either be plugins on their
>>own or more likely for XAP, integrated into a modulation section of
>>an "instrument".
>>
>
>Exactly.
>
>Unless I'm missing something, all you need for this is a way for
>plugins to keep track of the tempo (sync) and musical time (lock).
>The TEMPO + POSITION_* event set I proposed should be sufficient for
>for sample accurate lock to musical time, even accross tempo changes
>and transport skips.
>
Ok, fair enough. Yes, the approach you outline above seems reasonable.
>>>are plenty of parameters which might need some time indications
>>>but which are completely unrelated to notions of tempo. I'm
>>>thinking mostly about LFOs and other modualtion sources here
>>>(although there might be good grounds for lumping these in with
>>>frequency controlled parameters.) Just as I would rather
>>>
>>yes, sometimes you might want to control them quite independently
>>of tempo. but lots of the most interesting instruments in the
>>software synth world now allow tempo sync as an option, and its
>>very nice to have it available.
>>
>
>It is not just "very nice"; it's a required feature, IMNSHO.
>
Right.
>And it should preferably be sample accurate, and capable of tracking
>even the most furious tempo maps. Someone will complain sooner or
>later if they aren't.
>
Absolutely.
>see pitch control make as few assumptions as possible about tuning
>and temperament, I would like to see time control make as few
>assumptions as possible about tempo and duration. Sequencers
>generally do operate within the shared assumptions of traditional
>concepts of periodic rhythm, but in a lot of music (from pure
>ambient to many non-Western musics to much avant-garde music)
>such notions are irrelevant at best.
>
>>true, and i've been known to make this point myself. but the fact
>>that there is a lot of music in which periodic rythmn is irrelevant
>>doesn't erase all the music in which its a central organizing
>>principle. coming up with an API that doesn't facilitate periodic
>>(even if highly variable) structure when arranging things in time
>>makes working with such music more cumbersome than it need be, some
>>of the time.
>>
Point taken.
>I would like to clarify something here: musical time as used in an
>API is not by definition "periodic". (That's just an interpretation
>of it, normally based of the time signature.)
>
>The APIs that don't use audio frames for timestamps and song position
>generally use "ticks". 1.0 per quarter note is a fine unit, for
>example, if we (like practically everyone else) decide to use the
>quarter note as the base. It's rather handy, because a quarter note
>is always a quarter note, but a bar might be anything...
>
Well, not necessarily! A quarter note is not always the unit of a
single beat. In traditional
music theory, 6/8 meter is frequently thought of in 2 - the
dotted-quarter note gets the beat.
Half-note based meters (2/2, 3/2) are also very common, and things like
5/16 are not
uncommon in modern music. That said, I think what you mean by
quarter-note is
what I would call "counting unit" or "durational unit" or something like
that.
> while you can just modulate some audio with
>(sin(musical_time * M_PI * 2.0) + 1.0) or whatever. ;-)
>
Nice. Sounds like fun.
>
>
>//David Olofson - Programmer, Composer, Open Source Advocate
>
>.- The Return of Audiality! --------------------------------.
>| Free/Open Source Audio Engine for use in Games or Studio. |
>| RT and off-line synth. Scripting. Sample accurate timing. |
>`---------------------------> http://olofson.net/audiality -'
> --- http://olofson.net --- http://www.reologica.se ---
>
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