User guide

Viz Engine Administrator’s Guide

the audio device(s) listed in the configuration file’s SECTION AUDIO_CONFIG. By default

a one to one channel assignment from the first audio device is done when a new device

is selected.

7.3 Timing Behavior and Delay Settings

In this timing behavior for every activated DirectSound only card can be set. The

default values should work for most devices; however, differences may occur.

Latency adjustment on the DirectSound audio device

All sound devices use a Ring buffer that stores data until it is sent out to the audio

channels, and this ring buffer is organized in blocks of data. All sound hardware defines

a distance in blocks (or bytes) that needs to be maintained. For almost all devices

on the market a distance of 6 blocks is sufficient to have a “clean output” without

artifacts.

Tip: Try to decrease the BlockReadForward value down to 3 to accomplish

less delay for the output. Viz Engine creates a ring buffer of 1 second which

is split in 60 blocks. This gives an output delay of 10 milliseconds when

the BlockReadForward value is 6 (see the configuration file’s SECTION

AUDIO_CONFIG).

Matrox input and output buffer

Note that an unsynchronized audio card will always run faster or than a synchronized

video or audio card. There is a mechanism needed to keep all audio cards synchronized

with each other. The mechanism shown in Figure 21: Matrox input and output buffer , is

used by Viz Engine to fulfill this condition.

After mixing the packages received from the Matrox or Targa board the blocks of audio

data are moved to the Matrox output buffer. This buffer is organized as a ring buffer