Townshend Computer Tools DAT-Link - 9.2 Multiple Unit Recording; 9.3 Multiple Unit Playback

9.2 Multiple Unit Recording 83
above, the output from both units will start within one sample time of each other,
and op erate at exactly the same sample rate. Note however, that until playback
begins, there will not be any output from the digital outputs. Once playback b egins,
it may take a few seconds for the receiving DAT machine to lo ckonto the signal.
The same method can be used to synchronize recordings from multiple DAT-Links .
This version DAT-Link always outputs a zero on its digital output just b efore
beginning a recording. Thus, input can b e synchronized by using the sequence:
naset -u foo:0 -S E
naset -u foo:1 -S E
narecord -u foo:0 file1 &
narecord -u foo:1 file2 &
naset -u foo:0 -S OG
The rst two commands will turn o the output clocks for b oth DAT-Links . Since
they attempt to send a zero on their outputs, both units will block after the
narecord programs are begun. When unit 0 is changed to a master clo ck source,
both units will simultaneously b egin acquiring data from their inputs.
The above techniques can be extended to synchronize anynumber of DAT-Links ,
even units connected to dierent hosts.
9.2 Multiple Unit Recording
The program dlmrec provides a facility for synchronizing and recording from mul-
tiple DAT-Links . Although the same functionality is provided by using multiple
invo cations of netaudiod and narecord , as describ ed ab ove, dlmrec can obtain
signicantly b etter data throughput. This allows a greater numberofchannels to
be recorded simultaneously while handling synchronization transparently.
The recorded signal from multiple DAT-Links is stored in a single le, specied on
the command line, using one of two formats. The interleaved format, sp ecied
using the -I option to dlmrec , stores the same samples from eachchannel together
in the le. For example, if 4 DAT-Links are used for recording, the resulting le
will b e organized as shown:
L
0
0
R
0
0
L
1
0
R
1
0
L
2
0
R
2
0
L
3
0
R
3
0
L
0
1
R
0
1
L
1
1
R
1
1
:::L
2
N
R
2
N
L
3
N
R
3
N
(9.1)
where L
j
i
is the j -th left sample from DAT-Link unit j and R
j
i
is the j -th right
sample.
The second format, which is the default, is a blo ck-interleaved format and is de-
scribed in App endix B.1.9. Use of this format results in signicantly less CPU load
during recording since no reorganization of data is required by the host CPU.
For example, the command: