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quick question about latency

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quick question about latency

Postby adri » Wed Mar 14, 2018 4:34 pm

I and other people who played my organ noticed a slight delay in the time between the pressing of the keys and the sound. Like a pneumatic organ. haha.

I recently got a new soundcard, Fireface UCX. Can I safely set the latency to 256 in my sound card software? Or even lower?

Even for large organs? I have 64GB RAM and a very fast quad core processor.

Any further advice for my settings?
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Re: quick question about latency

Postby jkinkennon » Wed Mar 14, 2018 10:37 pm

If you are getting clean glitch-free audio at 512 samples then changing to 256 would be the equivalent of the pipes sounding about a meter closer to the listener. In other words, any audible latency would be coming from some other part of the chain between the key press to the audio being heard.

I've heard audible latency when using Reaper without arming the main HW track for recording. Never figured out why. I've heard audible latency with daisy-chained keyboard encoders. Also, excess MIDI messages such as might be generated by a dirty potentiometer or intermittent contacts (keys, pistons, stops) could overwhelm a conventional 5-pin MIDI circuit and cause buffering delays. Anything overloading the CPU as monitored from the HW Audio Meter?

All latency from encoder debouncing, excess buffering, MIDI regeneration (MIDI thru), PC delays, sample size, sample set delays, and speaker distance will add together to an overall latency. Somewhere around 30 to 50ms would be my guess as to what becomes audible. I've seen debouncing alone in some Arduino and Teensy sketches that border on audible with no other delays! They do have improved debouncing librarys now I think.
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Re: quick question about latency

Postby mdyde » Thu Mar 15, 2018 6:32 am

Hello Adri,

The first thing to do is to check that your PC is performing properly for real-time low-latency audio. The following utility should help to identify whether that's the case:

Leave it running (but without Task Manager being open) for half an hour or so whilst Hauptwerk is running with an organ loaded. LatencyMon needs to report that the PC is performing well enough for real-time audio before the PC will be able to work reliably for Hauptwerk (or any other real-time audio applications) at low latencies.

If it finds a problem, then please see this post for my suggestions to help resolve that: viewtopic.php?f=3&t=16674&p=125702#p125702 . (Francois Ratte in Canada also provides one-to-one remote assistance to resolve PC audio/MIDI performance issues on a consultancy basis: . He's very helpful and knowledgeable.)

If it does report that all is well, then by all means try setting the buffer size to 256 on Hauptwerk's 'General settings | Audio outputs' screen (rather than in your RME's control panel, since Hauptwerk's setting should usually override the latter). My experience is that RME's drivers and hardware are usually easily able to perform well with a buffer size of 256 (provided that the PC itself is performing well enough for real-time audio, as above).

A computer will inevitably achieve less polyphony (before audio glitches start to occur) at smaller buffer sizes that with larger ones, so you will probably need to set the polyphony limit a bit lower with a buffer size of 256 than you would with a buffer size of 1024 (for example).

With a good audio interface (such as your RME) a buffer size of 256 should result in about the same amount of latency as sitting approximately 2 metres from the mouths of the pipes of a real organ. Hence very few real organs (even tracker organs) would have a perceived latency less than that. 256 is the smallest buffer size that Hauptwerk allows for that reason (and since buffer sizes smaller than 256 are extremely demanding in terms of the real-time performance of all of the components and drivers in the computer, and strongly reduce achievable polyphony).
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