REAL-TIME AUDIO OUTPUT HINTS FOR CSOUNDAV
Art Hunkins - April 2005

1) The only flag you *need* for real-time audio is -+P. This specifies
Portaudio, which includes all MME, DirectSound and ASIO drivers in your
system. This flag is the equivalent of -odac or -odevaudio in canonical
Csound. You can enter any flag either on the command line, or under
CsOptions toward the beginning of a .csd file (use a text editor, such as
Notepad).

2) If you want MIDI input, you also need the -+K flag. This corresponds to
the -M flag in canonical Csound.

3) When you render files with these flags, a popup window will appear for
each flag. It will list available output drivers for -+P and MIDI input
devices for -+K. Once you have made your selections (and find they work),
you can optionally add the appropriate number to the flag (again with a text
editor) - e.g., -+P6 or -+M0. This will eliminate the popup windows.

4) With respect to latency (response lag to performance action, such as a
MIDI keypress): ASIO and DirectSound drivers give more accurate timing than
MME. However, these drivers are also more prone to pops and crackles; be
sure to close other processes running on your computer, including those in
the taskbar. The only processes that *must* remain open are Explorer and
Systray. Other than change driver type, there is nothing in CsoundAV you can
do to lower latency.

5) Also to minimize pops and crackles: it is recommended you eventually add
the following combination of flags (they suppress messages): -+Om0. Or, add
this longer combination (which also suppresses function table displays and
minimizes the GUI run-time window): -+Om0d+M.

6) If you're getting "zipper noise" when using an MME driver, either switch
to another driver type or do the following: in the AV's GUI window, click on
"Set Environment Paths," then insert a value of 50 or so (adjust as needed)
for "Portaudio output latency." This "zipper noise" is a new "feature" of
v0.0432 (and affects MME drivers only). It did not exist in 0.0431, which is
still available and near identical (http://sourceforge.net/projects/csoundav
- then click on "View ALL Project Files").

For console (command-line) AV, the solution is a bit more complicated. If
your OS is Win95/98/ME, edit your autoexec.bat file (in Notepad) by adding
the line:
set PA_MIN_LATENCY_MSEC=50
(This adds 50ms of latency to hopefully get rid of your "zipper.")
Comparably, in WinNT/2000/XP, right-click on your desktop "My Computer"
icon, and click on the "Advanced" tab of the "System Properties" dialog box.
Then click on the "Environment Variables" button and add a
PA_MIN_LATENCY_MSEC variable with the appropriate value (50 or so).

7) If you are *still* getting pops and crackles, you can try three
additional remedies: a) perform a MIDI version of a work rather than one
that uses a mouse clicking on-screen widgets (mouse motion is a major source
of pops and crackles). b) Assuming a sample rate of 44100, reduce this
number to 22050 and cut the value of ksmps in half (again toward the top of
the .csd file). With this option, sr, kr and ksmps must remain integers, and
kr * ksmps must continue to = sr. (Note that a lower sr will give
satisfactory sound for some works but not for others.) c) If available,
perform a "simple" version of the work that is less computationally
intensive, or one that requires fewer voices.

8) Otherwise, you need a faster computer. Most of the above suggestions will
"tweak" output, and get rid of the occasional pop or crackle (or consistent
"zipper"). Only a more powerful system will remedy sound that is
significantly choppy.


Some of these suggestions are taken from an email reply by Gabriel Maldonado
to the general Csound listserv on 3/27/05. I reproduce it below verbatim:


Have you tried with Portaudio drivers (-+P flag) only???? You don't have 
to set any other flag (except -+K for midi). So you only have to set -+P 
-+K and nothing else (eventually -+Om0 to suppress messages to the 
console, but only when you are sure yor csd works ok. DON'T SET ANY 
OTHER FLAG!!!). SB Audigy should allow a very low latency (in the order 
15-20 ms or even less) with the ASIO native host. You can tweak the 
latency by opening the "set environment dir paths" dialog-box and set 
the "Portaudio lantecy in millisecs" number boxes. If you get the 
message "PortAudio not initialized" try to change the sample rate (it 
seems to me that Audigy only allows 48 KHz, or 44.1 KHz under ASIO, but 
I don't remember). BtW Creative ASIO driver of SB Audigy are is stereo, 
no multichanneling (at least it is what I remember, maybe things have 
changed).  If you want to do multi channeling with ASIO, you should 
install (at your own risk) the KX driver:

http://kxproject.lugosoft.com

If you want an even lower latency (in the order of 5 ms) and reliability 
I suggest a professional audio interface (I have a MOTU 828 firewire 
that works very well with my laptop, but I was told that the best, 
concerning latency, are the RME Hammerfall interfaces). Notice that 
Windows is one of the worst OSs for reliable realtime tasks. You should 
be sure that your audio interface doesn't share IRQ with other devices 
for the maximum of reliability. Unfortunately this is not always 
possible with Windows-based laptops.

good luck!

Gabriel


Gabriel Maldonado
http://csounds.com/maldonado