How to measure audio performance

Equipment and methods

Abstract

According to my observation, in the audio scene there are two fractions: Subjectivists and objectivists. The Subjectivists claim that the ear can best judge audio performance and the objectivists claim that metrics matter most. I'm somewhere in the middle between both positions.

The objectivist part of me is highly interested in how well the equipment I build performs in terms of usual audio metrics. In this article I will explore options and methods to measure audio equipment performance.

Professional measurement equipment

Professional measurement equipment offers stellar performance, but is totally unobtainable for DIY audio enthusiasts. The Audio Precision APx555 costs around 28000 USD and this is well above the budget for any DIY audio hobbyist.

Semi-Professional measurement equipment

I came across the Quant Asylum QA402 audio analyzer, which sells for only 500 USD.

Here is the predecessor product QA401 review on Audiosciencereview.

There is also a discussion about the QA401 on DIYaudio.

Quant Asylum also provides dedicated software along with their products.

While audio performance of the QA401 does not seem to be that exciting, it has some compelling points like wide input voltage range and differential inputs and outputs.

Sound cards as measurement equipment

Using a sound card for doing measurements seems tempting because a good sound card may already be available and this would double as measurement equipment free of charge. A sound card is designed for low voltage level input and output and this restricts the measurement range to line level signals. For testing power amplifiers, an attenuator network would be required at the sound card input.

I investigated some sound cards for building my own budget measurement setup and found the audio performance to be totally unsuitable. I had the ESI U24 XL at home, which fails to meet even the most basic audio quality standards. I bought the Focusrite Scarlet 2i2 because I heard positive reviews from DIYers who used this sound card for doing measurements. I found the Focusrite sound card to be only marginally better than the ESI and returned it. Sound cards are simply not designed to deliver performance high enough to be used as measurement equipment.

In case the device under test has significantly more distortion than the sound card, sound cards may still be an option. For example for measuring loudspeakers.

I came across a more promising audio interface however: The E1DA Cosmos ADC. As the name implies, this is an ADC only, but designed to be suitable for measurements. Here is a review of the E1DA Cosmos ADC. And there is a discussion about the E1DA Cosmos ADC on Audiosciencereview. According to the review, performance looks good. The only drawback is the low input impedance. For measuring power amplifiers, an active super low distortion preamp that accepts high voltage input and can feed the low input impedance of the ADC would be required.

Signal generators

Samuel Groner has made a helpful comparison of low distortion oscillators.

Software

Audio Precision supports sound cards as measurement equipment and recommends this only for applicatiuons where the device under test has significant more distortion than the sound card, like loudspeakers.

I find REW easy to set up and use. While REW is optimized for room acoustics, it can also be used for some general audio measurement setups.

AudioTester is another option I haven't had a closer look at yet.

Conclusion

It is no surprise that good measurement equipment costs accordingly. I haven't found a solution for myself yet and see this artcle as scratchpad listing some options. Maybe this is also helpful for you.