linuxaudio.org

>> Now, for your rolling transport counter code...

quoted text
>>

>> 262        pos->tick += (int32_t)

>> 263            (nframes * pos->ticks_per_beat * pos->beats_per_minute

>> 264                            / ((double)pos->frame_rate * 60.0f));

>>

>> I think this suffers from truncation error.  It assumes that

>> whenever the tick changes, it is perfectly aligned with

>> frame 0 of the current cycle.  If nframes << frames_per_tick,

>> I think it'll get stuck.  To un-stick it, you may want to

>> keep track of the bbt_offset.

>>

>> Hope this helps,

>> Gabrial

>

>

> can't say i exactly understand this bbt_offset. i'd already seen it in

> the jack docs, and not really made sense of it there... but i've not

> seen it used in source code in various sequencing/timebase apps and so

> assumed i didn't need it either !???

>

I've been looking back over at those source codes...
Using a low ppqn such as 24 in my timebase code (based on

non-sequencer) utterly fails. Using a ppqn of 100 in non-sequencer

fails too. As does using a low ppqn in Dino.
(I see you've used a low ppqn of 48 in Tritium/Composite, and are

using jack_position_t::bbt_offset)
In other words, you're right about it sticking when nframes <

frames_per_tick and needing bbt_offset. Until now I did not realize

this is worked-around by using a high ppqn such as 1920 or 2520 (which

give integer results when divided by integers up to values 8 and 9

respectively (ie what the magic number means)).
So with low ppqn values, the bbt_offset integer will be ok, but what

about for high ppqn values?
Even high ppqn won't be perfect, but might not a floating point

bbt_offset improve the timing?*
*not in my case, it's some more serious problem in my code.
Cheers,

James.
>> [1]

quoted text
>> http://gitorious.org/composite/composite/blobs/master/src/Tritium/Tritiu...

>>

>>  http://gitorious.org/composite/composite/blobs/master/src/Tritium/src/transport/TransportPosition.cpp

>>

>>  http://gitorious.org/composite/composite/blobs/master/src/Tritium/test/t_TransportPosition.cpp

>>

>

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