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Re: [fluid-dev] Akai EWI-USB, Raspberry-Pi, and FluidSynth

From: laalaa
Subject: Re: [fluid-dev] Akai EWI-USB, Raspberry-Pi, and FluidSynth
Date: Mon, 16 Nov 2015 17:13:33 +0800


By definition latency means the time difference between the "action begin" and 
"sound begin".  Applying to this case, "action begin" is "begin blowing" or 
"clapping hand".

As a result, a precise way to measure the latency of wind controller would be:

1. You need a stereo recorder, one channel (mic) close to the mouthpiece, 
another channel (mic) close to the speaker.
2. When begin blowing, one mic recorded the 'very little wind' noise.
3. After some time, another mic recorded the speaker out.
4. Use some audio editing tools to see the waveform for the latency.

This was what I attempt to do with my Digital Piano (record keyboard instead of 
monthpiece, of course) and Fluidsynth output.  Though not success since I only 
have an iPhone to treat as a mono recorder.


> Date: Sun, 15 Nov 2015 07:19:18 +1100
> From: address@hidden
> To: address@hidden
> Subject: Re: [fluid-dev] Akai EWI-USB, Raspberry-Pi, and FluidSynth
> Hi all.
> How do you measure latency with a wind controller? I decided to try the
> "record the actual sound and analyse" approach.
> I tried using a mic next to the mouthpiece to record my "pfft" (leaking
> out the side), and the synth-ed sound that followed. It was difficult to
> distinguish the sounds. I then tried tapping with my free hand on the
> recording PC's mic in sync with my "pfft", i.e. trying to tap and blow
> at precisely the same time. After a bit of practice I measured about
> 80ms delay.
> Then I got a real recorder and a clarinet and did the same "tap and
> blow". I got about 40ms for that.
> I know it's not very scientific, but I concluded that the traditional
> instruments have a delay before the sound is produced (maybe 40ms), and
> my synth increases that delay by about another 40ms.
> When I play the EWI, however, I can't say that I notice a delay. Maybe
> it is because my brain is used to the inherent delay in the traditional
> instruments???
> So, some questions:
> 1. How does one measure latency for a wind controller?
> 2. Does anyone have a HOWTO for a low latency implementation on a R-Pi?
> Ben
> On 01/11/15 10:52, Peter Billam wrote:
> ...
>> I'm using a preempt-rt enabled kernel with hand-optimized IRQ
>> priorities and that gives me a latency (from key press to start
>> of sound) of about 12-15ms, which is acceptable.
>> On an ARM: yay! well done. At
>> http://www.pjb.com.au/midi/osdc/index.html#03
>> I reckon
>> About 10 milliseconds latency is acceptable. Of the linux synths,
>> TiMidity doesn't meet this; fluidsynth maybe just meets it,
>> on a fast CPU.
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