Townshend Computer Tools DAT-Link - 5.13 Buffering of Audio Data; 5.14 Customizing the Configuration

5.13 Buering of Audio Data 59
5.13 Buering of Audio Data
This section describ es how the DAT-Link buers audio data internally. This in-
formation may be useful in some interactive applications where it is imp ortantto
control latencies when sound les are played back. It may also be necessary to
modify the buer settings to avoid underrun errors when transferring audio les
across a network.
The DAT-Link contains an internal buer of approximately 2 Mbytes that is used to
buer audio data sent from the host computer. This buering is necessary to allow
the host computer to be used by multiple users and tasks without creating gaps
in the playback. It does, however, o ccasionally create some delays and unexpected
behavior.
When the host computer b egins sending audio data to the NetAudio server for
playback, the DAT-Link does not immediately b egin sending the data to its digital
audio outputs. It instead stores the data in its internal buer. Playback does not
actually commence until one of the following situations occur:
1. Enough data for one second of playback has b een transferred. The amount
of buering may be changed by using the bufferTime option described in
Section 5.14.
2. The host computer nishes sending the audio data.
Once playback b egins, the host computer must continue to send audio data to the
DAT-Link suciently quickly to keep the buer from b ecoming empty. If the buer
drains completely before the host computer is nished playing back a le, an error
is returned and playback is stopped. Gaps will never be inserted into the playback.
The buer utilization can be monitored by the nastatus command described in
Section 10.2.
The main eect of the buering on naplay is that there is a delay of approximately
0.5 seconds between the time the naplay command is issued and when sound output
begins. The actual delay time dep ends on the sp eed of the host computer, the SCSI
bus transfer sp eed, and the network load if the naplay command is issued on a
remote machine.
For applications where ner control over the buering is required, custom programs
can b e written using the subroutine library described in Section 12 and Appendix
G.
5.14 Customizing the Conguration
Many of the command line options, as well as additional options can be specied in
the users .datlinkrc le in their home directory. The format of this le is describ ed