Created on 2009-01-08 19:23:00

Question

How do I do a channel ID test on an APx585? Using the TestChannel button in Signal Path Setup seems to be a manual operation only.  That is, I have to click the channels one ata time and observe the result.  I’mlooking for an automatable test—one that I can put in a sequence and get apass/fail result on.

Resolution

If you are testing a device like an AV receiver with a Dolbyor dts decoder in it, the Audio Precision Blu-ray disc (APx-BD1) contains encoded waveform files that were constructed specifically for this purpose. These encoded files can be downloaded from our web site.

If your signal path does not include a device that doesDolby or dts decoding, the process is less direct. Linear PCM files are2-channel (stereo). You can create four stereo .wav files, each containing apair of different tones, and then map them to appropriate channels. When usingthe linear mode the system can only test two channels at a time, but you canstill automate this by having four instances of the frequency measurement inyour sequence.

For example, see the APx project file named APx585 ChannelID.approj. This project contains one signalpath with 4 instances of the frequency measurement named Ch 1 & 2, Ch 3 & 4, etc. For each measurement, a .wav file has been created with uniquetones that help to identify the channel. Each waveform has tones at two distinct frequencies, labeled Tone 1 and Tone 2, as listed in Table 1. Tone 1is the main tone, with a level 20 dB higher than Tone 2. Tone 2 is at a muchlower frequency than Tone 1, and it is included in case the channel beingtested in the DUT contains a low pass filter (e.g., a subwoofer or LFE channelin an AV receiver). This way, if the low pass filter eliminates the main tone, thesecond tone is still available for identification purposes. This same scheme isused for the Channel ID files on the AP Blu-ray disc noted above.

In the project file (APx585 Channel ID.approj), in each ofthe four frequency measurements in Signal Path 1, the appropriate generatorchannels have been enabled and measurement limits equivalent to the Tone 1frequency ± 5 Hz have been set.Hence, if you run the sequence, the report will indicate a Pass result if thechannel outputs are connected to the correct inputs. In the project file, thesignal path has been set to Analog Balanced Output and Analog Balanced Input,so that the 8-channel loopback cable can be used for convenience. This is justfor illustration purposes, and you should change this to suit the DUT.

This approach can be used with any instrument in the APxfamily, and customized appropriately. The individual waveform files are alsoincluded for the convenience of users who want to make their own project file.

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Ref:SLX3969 / Joe Begin

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