On Sun, 2009-01-11 at 12:26 +0100, Peter Plessas wrote:
Timing is a very interesting topic in pd (and with computers in general). When i try to measure the [realtime] of a [metro 4] object, i get: print: 11.351 print: 0.122 print: 0.11 print: 11.402 print: 0.088 print: 0.119 print: 11.374
I think you get the same values. Can it be true that there is a deviation of 7ms now and then? More interesting: Why is it not only now-and-then, but every fourth sample? So there must be some phase shift which accumulates in the operation of [realtime]. On averaging those values, one gets a value close to 4ms though. Does anyone know about the real-life resolution of [realtime]?
those time steps seem to be related to the audio driver. you seem to run pd on jack with a latency of 23ms / 512 frames per buffer @ 44.1kHz. when i use 2048 per buffer at 44.1kHz, i get 92 ms latency and the numbers look like this:
print: 0.048 print: 0.047 print: 0.033 print: 0.049 print: 0.05 print: 45.916 print: 0.04 print: 0.05 print: 0.051 print: 0.052 print: 0.035 print: 0.05 print: 0.064 print: 0.052 print: 0.032 print: 0.046 print: 0.048 print: 45.825 print: 0.033 print: 0.047
so, here every 12th number is significantly bigger than 0 and also here, this number is approximately the half of the latency. this behaviour seems to be typical for jack. when i run pd in windows in virtualbox, i get more random looking numbers.
i guess, if you want really accurate realtime values, you would have to go for the least possible latency, since it seems, that time of execution of pd is completely dependent on the audio driver. and even if this would cause drop-outs, the results of [realtime] wouldn't be affected in a way, that the overall measured time is still valid. if you use [timer], which measures logical time, and you get drop-outs, all dropped out time is not part of the measurement and you will get wrong (too small) values as a result.
i never understood, why [timer] is giving different values from the ones that you expected, when connected to a [bang~] inside a re-blocked subpatch. would be cool to have that either explained or declared as a bug.
roman
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