Hi everybody,

I use PD as part of my PhD project. Since audio/haptic asynchronity is an issue I have to keep latency down. My test subjects have to press buttons and virutally instantly hear the sound they triggered. The sounds are stored in arrays and played back using tabplay~
I have just checked the delay between the press of a button and the resulting sound. The buttons are connected to my computer using a custom microcontroller board which is quite common at my university and send the trigger command to a PD comport object. The baud rate is set to 230400 bps and only one byte is needed as command. Latency of the entire button-microcontroller-serial output should be way below 1 ms.
For sound output I use a Lexicon Lambda USB interface at 96000 kHz and 5 ms latency.
When I monitor the delay between physical trigger and output I get latency times ranging from just under 10 ms to over 25 ms. More annoyingly, this latency is not stable but but changes every time I trigger.
Since my "hardware" latency should be just over 5 ms and PD adds up to 20 ms to this I assume PD interally processes things at a certain framerate which should be arround 50 Hz or 20 ms. Is it possible to increase this framerate in any way?
The system runs on Ubuntu Studio 8.04, it would be possible to switch another audio interface (RME Hammerfall).

Any ideas are greatly appreciated.

Alex

i think the latency is probably coming from your linux sound driver. oss or alsa. whatever yoU're running.

for low latency the key seems to be to run pd in realtime mode (start pd with the -rt flag, i think you have to also add a sudo command to do that, so your startup would be something like sudo pd -rt ), and then run the jack audio driver.

that's what i have READ, countless times, but as i said i hate going near any of that stuff, and the jack interface window scares me

anyway, have a look on the ubuntu studio help/discussion forum. there are quite a few threads there about getting low latency.

(by the way, pd doesn't have a framerate as such for messages. they are processed as quickly as possible.)