Mixed-Signal Audio Tests using LabVIEW DAQmx and DigAudio

Publish Date: Nov 08, 2010 | 9 Ratings | 3.56 out of 5 | Print | 1 Customer Review | Submit your review


This example shows how to develop mixed-signal audio stimulus-response measurements. This application uses an NI-4461, 24-bit, 204kS/s analog audio generator/analyzer (programmed with NI-DAQmx) and an NI-7813R with the CB-2181 digital audio accessory for digital audio generation/analysis (programmed with NI-DigAudio, part of the NI AudioMASTER software platform) to test DAC and ADC characteristics like linearity, frequency response, or signal-to-noise ratio. The used unit-under-test (UUT) was a generic audio receiver/amplifier with both analog input/output and digital audio (S/PDIF) input/output connections.

1. Measurement Setup

The NI-4461 offers two analog output and two analog input channels which should be connected to the stereo audio (L+R) inputs and outputs of the amplifier respectively.  The digital audio output from the CB-2181 should connect to the optical digital audio connection of the amplifier and the output from the amplifier should connect back to the CB-2181 for analysis.  Typical consumer units use optical TosLink and/or coaxial RCA digital audio connections while high-end and professional equipment make use of balanced XLR connectors.

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2. Testing an Audio DAC

To test the quality of an audio DAC, you need to generate digital audio (SPDIF or AES3) into the receiver and analyze the analog audio being generated by the receiver.  To perform this test, the digital audio generator and analog audio analyzer must be tightly synchronized to measure the linearity and frequency response of the DAC.

In the block diagram below, you can see how the DigAudio VIs are synchronized with the DAQmx VIs for generation and acquisition.  For this example, we are computing the Power Spectrum, Magnitude Response, and THD of the audio signal that was processed by the DAC, which you can see on the front panel.

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Customer Reviews
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Synchronisation  - Feb 8, 2011

Very nice example, this is what I was looking for. However, there are a couple of questions: 1. Each task is given the same sampling frequency and triggered simultaneously using the PXI_Trig0 line. Is this enough to guarantee a correlated measurement over x-samples? Is there and drift here assumed? I assume the PXI-7813R and PXI-4461 clock generators are in sync and both phase lock looped to the 10MHz Backplane to prevent this? 2. All DA converters have delays built into them. Would it be possible to include an input-output phase relationship into this example, taking into account the delay of the system!?

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