REAL-TIME AUDIO OUTPUT HINTS FOR WINDOWS VERSIONS OF CSOUND

REAL-TIME AUDIO OUTPUT HINTS FOR WINDOWS VERSIONS OF CSOUND
Art Hunkins – April 2005

For the Windows platform, the most responsive, versatile and user-friendly
of real-time Csounds is CsoundAV. Performers and relative newcomers to
Csound will experience fewer problems with CsoundAV compared to other
versions. (This is why CsoundAV is the preferred version for my real-time
compositions.) For extensive discussion of CsoundAV, as well as a general
orientation to real-time performance issues of Windows Csound, see my
article, “Real-Time Audio Output Hints for CsoundAV.”

CsoundGBS/flCsound–

CsoundGBS/flCsound Windows executables are located at:
http://sourceforge.net/project/showfiles.php?group_id=81968

The GBS version, currently GBS11, is command-line, while flCsound
incorporates a simple GUI. FlCsound is the more user-friendly for beginners.
With these versions, you need the following set of command-line flags or
CsOptions:
For files not using MIDI:
-m0d -odac
For files using MIDI:
-M0 -m0d -odac

The -m0d (composite) flag gets rid of messages and displays that can cause
clicks in real-time audio. You can modify CsOptions with any text editor,
such as Notepad. (CsOptions are toward the beginning of a .csd file.)

These examples of flags assume that you have a single audio output device
(and MIDI input device). Device numbers always start with zero. If you need
to specify a different device number, identify the appropriate number by
examining your message output (where they are all listed), and add it to
your flags (e.g., -odac1, -M1).

These versions are limited to stereo (MME drivers only).

Victor Lazzarini’s MyCsound4–

MyCsound4 is a command-line only version found at:
http://www.nuim.ie/academic/music/musictec/csound

Use the same set of command-line flags or CsOptions as given for the GBS/
flCsound versions above.

This version too is limited to stereo (MME only).

In either of these alternative Csounds, sonic output may be broken and
sporadic. The drivers they use are the older, higher latency (delayed
response) MME variety. *Adding a -b1000 flag to the command line or
CsOptions will likely help this*. You are urged to experiment with values of
-b from 1000 to 4000 to find the number that gives you the most click-free
and immediate audio response. (Lower values will give faster response, but
risk clicks and pops.) Also, closing as many concurrently running processes
in the background as possible will help avoid breakup. Note that the -B flag
is not used in either of these versions.

Csound5beta–

A new, command-line, *beta* version of canonical Csound:

http://sourceforge.net/project/showfiles.php?group_id=81968

Csound5 is the future of Csound, and is intended to be a (much needed)
cross-platform solution. Though it is presently considered beta software,
Csound5 for Windows is ready for real-time use. It requires ASIO drivers,
and will not work with MME or DirectSound; however, with the advent of
ASIO4ALL, this is no longer a problem (see below). The only real-time
limitation of ASIO currently is that it cannot do audio input and output at
the same time.

Here is list of items to observe with Csound5beta:

1) The author of ASIO4ALL (an ASIO driver for *stereo* soundcards) has
done a version that now supports SR’s below 44100 (down to and including
8000) – whatever your sound card allows. What this means is that real-time
pieces that “broke up” on slower computers can now be performed with
unbroken sound at slower SR’s for at least test/compositional purposes.
Here is the link to the test version (which will presently be incorporated
into a standard release):
http://www.asio4all.com/A4Av26p1.exe

The standard ASIO4ALL v2.5, limited to SR=44100 and above, is here:
http://www.asio4all.com/A4Av2Ins.exe
General information about ASIO4ALL (including a user forum) is available at:
http://www.asio4all.com

*Without* ASIO4ALL, stereo soundcards cannot run Csound5beta. *Native* ASIO
drivers are only available for multi-channel cards.

2) Istvan Varga’s Linux recommendations relative to -B and -b flags for
Linux (command-line or CsOptions) also work well for Windows. *Both -B and
-b must be specified* for realtime. -B is the more critical value. The
recommended flags:
For files not using MIDI:
-m0d -odac -B256 -b64
For files using MIDI:
-M0 -m0d -odac -B256 -b64

These values will work in nearly all cases. The only exception is SR (sample
rate) = 44100 and above on slower computers, where -B must be raised to
2048.

Note that -B should be larger (normally 4 times as large) as -b. (This is
not required, but works well.) Numbers are preferably powers of 2 (2, 4, 8,
16, 32, 64 etc.) This too is not required; Csound will actually adjust
values to make -B and -b some simple multiple of one another.

In general with Csound: Faster computers will permit smaller -B (and -b)
buffer values – thus lower latency, while slower computers require higher
values (resulting in higher latency). Also, the lower the SR, the lower the
buffer values can be (lower latency). Conversely, the higher the SR, the
higher these values may need to be (thus resulting in greater latency).

The above observations apply equally to native ASIO drivers as well as
ASIO4ALL.

When using ASIO4ALL, I recommend the following setup in its Off-Line
Settings (linked on the Desktop):

1) Disable selected sound card’s audio inputs.
2) Set ASIO Buffer Size to maximum (2048).
3) Set Kernal Buffers to maximum (4).
4) Turn off “Always Resample 44.1 kHz.”

These steps will eliminate/minimize broken sound.

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