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RE: [fluid-dev] How to optimize Fluidsynth latency in Windows?

From: EarMaster - Hans Jakobsen
Subject: RE: [fluid-dev] How to optimize Fluidsynth latency in Windows?
Date: Mon, 19 Apr 2010 17:04:37 +0200

Thank you Pedro. I have now measured the latency in Fluidsynth with two 
different audio interfaces in 48 KHz:

1) Realtek audio, 26 periods x 64 samples = 35 ms
        The actual measured latency = 80 ms
2) Alesis io2 audio interface, 26 periods x 64 samples = 35 ms
        The actual measured latency = 55 ms

Even though the theoretical latency should be the same with the two audio 
interfaces, the Realtek audio has an extra overhead of 25 ms compared to a 
quality audio interface.

This is interesting, but I believe most of my users will have the standard 
Realtek audio. If I could reduce the latency of the Realtek audio to 50 ms, 
then I would be satisfied.
The question is if it is possible?

PS. I use version 1.0.9 of Fluidsynth because it is the only one I have an 
interface for in Delphi. Are there any latency improvements in version 1.1.1 ?

Best regards,
Hans Jakobsen

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Pedro Lopez-Cabanillas
Sent: Sunday, April 18, 2010 2:13 PM
To: address@hidden
Subject: Re: [fluid-dev] How to optimize Fluidsynth latency in Windows?

>> The wiki page has specific tips for ALSA, but most of the information is 
independent of the platform. The most important factors that limit the lowest 
artifact free latency that can be achieved are:

1. The hardware audio device
2. The operating system drivers for the hardware audio device.

If you need professional quality, you need professional grade components.

I've tested FluidSynth 1.1.1 with two audio devices in my Asus laptop using 
Windows XP, and here are the results using 48 KHz (native sample rate). If 
you don't use a native sample rate for the audio device, the OS may need to 
resample the audio streams, using additional buffers and generating bigger 

* With the internal sound device, identified as "Realtek HD Audio", the 
minimum is 3 periods x 1024 bytes. Latency = 3x1024/48000 = 64 ms.

* With a set of external USB speakers, the minimum is 4 periods x 512 bytes, 
latency about 43 ms.

I've also tested in a friend's computer a SoundBlaster X-FI Titanium 
Professional, and for my surprise the minimum was 2 periods x 256 bytes, 
about 10 ms at 48 KHz. 

So, using DirectSound and the native sample rate of the audio interface it is 
possible to achieve low latency with adequate audio hardware and operating 
system drivers, even without ASIO (provided only by professional sound cards, 
anyway). The best settings depend on the audio card and drivers.

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