Townshend Computer Tools DAT-Link - 10.6 Interactive Playback of Multiple Files

10.6 Interactive Playback of Multiple Files 93
narecord -s 8000 -t 1 >/dev/null
The output of the command is not imp ortant, it just forces the NetAudio
server to load the appropriate lters.
2. Run the program nagetfilter with either the -P or -R option to acquire the
playback or record lter respectively. To continue the ab ove example, type:
nagetfilter -R >filter.specs
The output from nagetfilter are ASCII oating point numbers, one per line.
The rst line contains the sampling rate of the discrete-time lter's impulse re-
sponse. The remaining lines are the values of the sampled impulse response. This
impulse resp onse completely characterizes the DAT-Link 's lters. It can be used
as input to other analysis programs or custom software to derive the frequency re-
sponse of the system. An example script to do this conversion and plot the results
using MATLAB is included with the DAT-Link software. The script is called IN-
STALLROOT/etc/dl/plotresp.m , where INSTALLROOT is the directory where
the DAT-Link programs were installed. The plot generated byMATLAB after the
above commands are executed is shown in Figure 10.2.
10.6 Interactive Playback of Multiple Files
The xnaplay provides a simple interface to playbackmultiple les. It uses the X
Window System to display a control panel on the workstation screen with a number
of buttons lab elled with lenames. Clicking on any lename causes the le to be
played. An example panel is shown in Figure 10.3.
The xnaplay program is run with each lename to b e displayed as arguments. For
example, the panel shown in Figure 10.3 was generated using the command:
xnaplay mozart_orig mozart@64kbps beethoven speech_orig \
speech_LPC speech_CELP
When a button on the xnaplay panel is clicked, the naplay program is executed
using the named le as the argument. If it necessary to pass some ags to the
naplay program, such as setting the sampling rate, they can be sp ecied along
with the lename. The command
xnaplay '-s 8000 file1' '-s 12000 file2'
will put up a display with buttons labelled le1 and le2 , but the playback of
le1 would be at 8,000 samples/second while le2 will be played at 12,000 sam-
ples/second. Note that the quotes are necessary in the above command to group
the options with the appropriate le.