Subject: Re: [linux-audio-dev] XAP: a polemic
From: Tim Goetze (tim_AT_quitte.de)
Date: Mon Dec 16 2002 - 23:30:37 EET
Paul Davis wrote:
>>you absolutely need ppq for the tick system to properly map
>>different measures (5/4 time, 6/8 time etc) as per previous
>>post.
>
>well, if ppqn is variable, then sure. but cubase and all other vst
>apps have defined it to be 1, which makes it irrelevant. their "pulse"
>or "parts" (there seems to be disagreement over what the first "p" in
>"ppqn" stands for) is not the same as the "tick" are discussing,
>however.
it is ticks for all i know, spell it tpq if you happen
to like that better. have you ever parsed a MIDI file?
the same value is called 'division' in the file specs.
>so yes, ticks-per-beat is still necessary, but its a constant (1920 in
>ardour).
there's no point in limiting this to be a fixed value.
>>you're better off specifying tempo as quarter beats/minute
>>uniformly for the above reasons.
>
>what reasons? after 2 rounds of fairly intense discussion on
>ardour-dev, we could find no reason to favor quarters over any other
>value. it makes no difference unless all the music you ever want to
>handle uses quarters as the beat note value. since this is
>demonstrably false, there is nothing particular interesting about
>using quarters.
you're right, it doesn't matter what reference length you
choose. quarters simply happen to work well, and there's
no need to break with convention here.
>>add seconds-per-beat for plugins that are not limited to
>>audio purposes.
>
>but thats just a straightforward transform of samples-per-beat given
>samples-per-second, so there is no reason to specify both. either one
>seems equally good to me.
it must be assumed the hosts knows seconds-per-beat better
than the plugin. thus, forcing another calculation back
from frame units is illogical.
>>>the METER event needs to include
>>>
>>> beats-per-measure (floating point value) [ 3, 5, 7, 9.5 etc ]
>>> beat-note-value (floating point value) [quarter,1/16th, etc]
>>
>>i wouldn't make either a float, it is by far too uncommon
>>to be justified and makes some arithmetic cumbersome.
>
>what arithmetic is cumbersome? beats-per-measure has to floating to
>accomodate most non-western music, and if thats a float, you may as
>well make beat-note-value the same, to avoid constant casting back and
>forth.
one of the basic properties of rhythmn is that human beings
are able to count it, otherwise they cannot sync (groove)
to it. no musical tradition i know of violates this principle;
rhythmn is integral by its very nature.
i'd be happy to hear a good example proving this wrong. but
take note that i don't accept 1/2, 1/3 and relatives as
qualifying because they can better be (and usually are)
expressed using integer numbers.
about arithmetic: float operations, as you know, introduce
round-off error. integers can be used in accumulators with
much less inconvenience.
tim
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