[sdiy] Bunching of MIDI clock messages
21pointy at tpg.com.au
Thu Sep 19 04:39:28 CEST 2013
On 13/09/2013, at 3:28 AM, Colin f wrote:
>> On 12/09/2013, at 10:20 PM, Richie Burnett wrote:
>> Well, that's exactly what machines like Roland's TB-303, TR-606,
>> TR-808 and TR-909 actually do. Their tempo clock is a free-running
>> analogue oscillator that is polled every 2 milliseconds by the CPU,
>> and the instrument trigger pulses are then all generated
>> simultaneously for the appropriate instruments.
>>> And, before anyone says that it's the 2ms polling that's the
>>> problem... It has been implemented this way because the real
>>> instruments I'm modelling (TR-808 and TR-909) have a CPU that runs
>>> on a 2ms interrupt clock. All of their instrument triggers being
>>> synchronised to this internal 2ms interrupt clock. I'd like to
>>> retain this as it is one of the things that gives these
>>> instruments their much sought after "groove".
>> Nah, that's a myth.
>> Slop and randomness do not make a groove.
> Randomness may not make a groove, but a cyclic relationship between
> master clock leading edges and a polling CPU responding to them at
> points in its 2ms period can.
> Colin f
I appreciate you guys are talking at a technical level that is mostly
beyond my ken, but I'm very interested in the practical result.
So a free-running tempo clock gets polled 500 times a second by the
CPU, and this gives rise to a cyclic variation in an otherwise steady
Or, are you saying that the cyclic variation affects where exactly an
intrument is triggered on a given beat subdivision? Either way, it
would have the same effect.
OK, now if this cyclic variation was to have a constructive
contribution to a particular machine's groove, I would have thought
the cycle would have to affect some multiple of beat subdivisions that
recurred in one, or maybe two, bars of 4/4 time (these machines aren't
famous for their use in jazz time signatures!).
Years ago, before I adopted the Innerclock solution, I looked at tempo
clock stability in various machines here including the 808 and 909,
both in master and slave roles. I measured the number of samples
between consecutive quarter notes. There was both random variation and
cyclic variation, but the cyclic variation was odd-numbered, 9 or 7,
something like that. That sort of cycle would actually have a
destructive contribution to a 4/4 groove, worse than random, which is
why I've always thought the claims made about these machines intrinsic
magic/groove/feel/woteva were rubbish.
More information about the Synth-diy