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09 Oct 2015 - 20:26:23

Low-Cost Audio Testing Techniques Using a PC

RightMark Screen Showing Range of Audio TestsNot every audio test application needs the superlative performance of an Audio Precision 2722, particularly when the equally superlative price tag of nearly $30k has to be taken into account. It is possible to get very good results using a regular sound card and software like the freeware version of RightMark Audio analyser. This has opened up a whole world of objective testing and research for DIY speaker constructors and room optimisers.

Typical accuracies of +/- 0.5dB for level and frequency response can be routinely achieved and THD measurement down to the 0.1% level. Most of these limits are set by the performance of the computer sound card itself.

How PC-based Audio Analysis Works

To test any piece of audio gear it is necessary to generate a test signal, pass this though the device under test, and then process the output signal to come up with the measurement.

The typical PC sound card contains a digital to analogue converter which can be used as an accurate test signal generator, when controlled by the PC software. The sound card also contains an analogue to digital converter and signal conditioning hardware, which can be used to capture the output of the tested device. This is stored to the hard disk, and the software can process this in non-real time to produce a spectral display or audio measurement.

Engineers that have used professional audio test sets will of course miss the extensive balanced connectivity and the real-time display, however for DIY enthusiasts and prosumer applications the lack of a real-time display and the relative inaccuracy are a small price to pay for the cost benefits.

As an added bonus the PC software usually can display a spectral analysis of the signal, which can indicate the nature of any distortion. RightMark Audio Analyzer can even sweep the frequency response of something like a recorder, since the analysis process is synchronised to a start pulse in the test generator output, so non-real time signal paths can be processed. This was not easy to do using analogue test equipment in the past.

RightMark Audio Analyzer Freeware is Capable of Many Standard Audio Tests

As the initial screen shows (see photo) RightMark is capable of the following basic audio tests -

Frequency Response (multitone and work order management swept sine)Noise LevelDynamic RangeTotal Harmonic Distortion (THD)Intermodulation Distortion (IMD + Noise)Stereo CrosstalkImpulse and Phase ResponseThere are other alternatives, such as the Visual Analyser work order management Project that do a similar jobPC Baased Audio Measurement Software Delivers Good Performance and Low Cost

A 1dB accuracy for frequency response and 0.1% or better THD resolution are good enough for many applications, and this sort of precision can be achieved by a typical consumer-grade USB card like a Creative SoundBlaster Audigy.

Rightmark will support semi-pro non-resampling cards accessed via ASIO if better performance is needed. High-end performance is, of course, the domain of the likes of Audio Precision and similar companies' products.

PC-based audio measurement has opened a whole new world for DIY loudspeaker and audio designers to get objective measurements of their work, speeding up the development process and facilitating comparisons. This is pretty good for the $0 asking process and using the computer and audio hardware already owned.

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