QA403 Audio Analyzer: Affordable Precision for Audio Professionals and Hobbyists

A few years ago, the QA403 from QuantAsylum filled a gap in the market — positioned between audio analyzers priced like new cars on one side, and hobby solutions with sound cards or USB audio interfaces on the other. In this article, we investigate how the audio analyzer holds its own compared to other solutions.

Market Split in Two

It has been some time since I compared the QA403 audio analyzer from the U.S.-based company QuantAsylum with the current “gold standard” for audio measurements, the APx555(B) from Audio Precision. QuantAsylum has survived the coronavirus and chip crisis and apparently sells the QA403 (see Figure 1) in considerable quantities, and the software is continuously updated. When I wrote the Elektor article back then, I found the hardware and software so good for the price that I bought the device provided by Elektor (even before the test ended).
  A few years later, it is worthwhile to take another look at the market for audio analyzers. This market is still divided into two segments: first, devices specifically designed for measurement, and second, sound cards or USB audio interfaces, which become measurement devices only when used with special software — meaning you have to accept certain limitations.

The professional measurement devices are usually built as a “black box” with no controls other than the power switch, and only become a measurement device when used with a PC and their dedicated operating software. Input and output levels are, as usual for measuring equipment, calibrated and offer a wider adjustment range.

The Gold Standard

The professional audio analyzer market continues to be dominated by Audio Precision and its products. The APx555B remains the best you can buy; however, prices are so high that such a device is out of reach even for the most dedicated hobbyists.

Other well-known measurement device manufacturers have exited the market because their products could not match the quality of Audio Precision and were not significantly cheaper either. That leaves the option to look for used devices. However, prices are still high, and it is clear that these devices are no longer maintained or repaired. Given the cost of repairs, a defect is usually a “total loss.”

Audio Measurements for Beginners

For those new to audio measurement technology, using a sound card or USB audio interface with third-party measurement software — which is usually available at least in a basic version for free (see the “Measurement Software for Audio Interfaces” text box) — is a good place to start.

The range of such USB audio interfaces and sound cards is very large, making it difficult for beginners to get an overview. In any case, it’s important to realize these devices were designed for recording and playing music, not for measurement purposes.

The input and output levels are not calibrated; you must set them (for example, with the help of an oscilloscope) using the controls on the audio interface or its software. Direct adjustment via the measurement software is not possible.

Moreover, since the permissible levels at the audio interface are low, you have to use external amplifiers and attenuators. Some of my students managed to destroy three external sound cards when measuring an audio power amplifier because the input levels at the sound cards were too high.

An important criterion here is the power supply for the internal amplifiers of the audio interface. In the simplest case, the 5 V from the USB connection is used, ideally after a low-dropout regulator. This means output signals are limited to about 3 Vpp, and significant distortion (THD) occurs above 1 Vpp. The same applies to the inputs.

The situation is somewhat better if a symmetrical supply of ±5 V is used. However, manufacturers usually provide no information about the internal design of their devices. Either you open the device, or you measure the maximum levels and try to infer the internal power supply from the results.

By contrast, the QA403 audio analyzer is also powered via USB, but its op-amps are supplied with ±15 V, generated by DC/DC converters.

Now let’s talk about quality. Essentially, there are two types of measurements for which you want to use an audio analyzer. These are frequency responses (level over frequency, linear or logarithmic) and measurements of distortion and noise (THD, SNR, THD+N). The former are no problem with a modern USB audio interface plus external measurement software. When it comes to distortion, however, this is where the wheat is separated from the chaff. A loopback measurement — which you should perform at different levels — gives insight into the quality of a USB interface or any audio analyzer. Optimal adjustment of the digital drive of the internal DAC and the input level requires some experimentation! In general, significant distortion and noise levels cannot be compensated for by even the best software.

Measurement Software for Audio Interfaces

To my knowledge, there are three different PC programs that can turn an audio interface into a measurement device: ARTA, REW, and AudioTester V3.0. I personally prefer to use the latter; however, the author is now retired, and support was discontinued in mid-2025. His former website is no longer accessible. The same goes for ARTA—the latest version is now freeware. That leaves only REW, with which I have little experience. At least REW (in the basic version) can be downloaded for free [3].

The QA403 Audio Analyzer

The QA403 is still the entry point to professional audio measurement technology. Given its performance, it is still an affordable device despite its price (€799 at Elektor). In my opinion, it also makes sense to buy it from the only European distributor — Elektor. You could, of course, order it directly from the manufacturer in the USA, but then you have to pay for shipping, import tax, and customs fees. If there is a possible defect, it is also easier and cheaper to send the device to the distributor in Europe than back to the USA.

My QA403 is always ready to go on my equipment shelf and is quickly set up. The software is simple and intuitive to use, even after a long break. Recently, I used the compact device to measure a 40 kHz high-pass filter for my new ultrasonic transducer. Figure 2 shows the test setup.
 

Figure 3 shows the frequency response with a linear frequency scale, and Figure 4 with a logarithmic scale.
 

You can also get an overview using white noise (Figure 5).

Figure 6 shows a loopback measurement in which an input is simply connected to an output: The loopback spectrum of a 1-kHz test tone at 0-dBV amplitude.

The QA403 is now in use by many audio enthusiasts, and naturally, there are points of criticism from the community. The BNC jacks and lack of XLR connections are often mentioned. Given the size of the enclosure, I think the BNC jacks are appropriate. There are good adapters for RCA and adapter cables for XLR or jack available, or you can make them yourself (for example, from BNC cables).

XLR connectors would require a larger device, but then you could also include the option for an external power supply. The device draws up to 1 A from the USB port, so a good USB cable is important. Fortunately, the bottom of the screen tells you how much current is flowing and what voltage is still reaching the device; you can use this information to sort your USB cables. (In my own experience, the cables that look robust are not always the best.)

For me, it is remarkable that the up-and-coming Chinese manufacturers of measurement devices have not yet entered this market. So the QA403 seems to be holding its own in its market niche. My clear conclusion: If I didn’t already have one, I would buy a QA403 again in a heartbeat!

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Editor's Note: This article (260084-01) appears in Elektor May/June 2026.