Fresh From the Bench: Listen SoundCheck and AmpConnect 621 Audio and Acoustics Test Suite

The latest version of Listen’s flagship audio test software, SoundCheck 21, allowed audioXpress to review also the latest Listen AmpConnect 621 USB-controlled multichannel audio test interface. The innovative algorithms and increased measurement capabilities of this powerful and flexible software, together with the AmpConnect 621 analyzer, combines all the functionality required for audio testing in the lab bench or in the production line. This article was originally published in audioXpress, March 2024.

When Listen released SoundCheck 21, the latest version of its flagship audio test software, audioXpress scheduled this review, which also allowed us to try the latest Listen AmpConnect 621 USB-controlled multichannel audio test interface. The innovative algorithms and increased measurement capabilities of this powerful and flexible software, together with the AmpConnect 621 analyzer, combines all the functionality required for audio testing in the lab bench or in the production line.

Photo 1: I received Listen’s full suite prior to conducting the SoundCheck 21 review.

Any development in audio and acoustics requires proper measurement suites to document progress or to verify performance, both at the development stage and in production environments. You do have a choice from different brands, which all have a slightly different focus. However, since 1995,
Listen, Inc. has offered a complete hardware and software palette that can be flexibly tailored to its users needs, and it is primarily aimed at production environments.

System Setup

Prior to the review, I received a complete hardware and software suite, with all the options enabled. This is what a prospective customer would receive to test it and see if it meets their needs, and which options they do and do not want. As we will see later, the structure with many options and attendant pricing has both advantages and disadvantages.

The complete set reviewed here contained the full SoundCheck 21 software suite, an SCM microphone kit, and the AmpConnect 621 interface hardware (Photo 1).

SoundCheck Software

The software is organized around a dashboard where you find all the usual functions, such as generators and multiple instrumentation options.

Dashboard and Instruments. Once on your dashboard screen, you can define the available functions by dragging and dropping instruments as well as sequences. All the usual bench tools are available, such as signal generators, frequency counters, an oscilloscope, and spectrum analyzers.


Figure 1 shows a sample dashboard that we used. You can combine instruments with test sequences that we haven’t seen before but have turned out to be extremely practical. It’s a busy picture so take the time to review it, we found this setup quite practical!


Figure 1: Here is a typical SoundCheck dashboard with instruments and test sequences loaded.

Sequencing Functions. As a first typical test, I connected a compression driver to the AmpConnect hardware and ran the provided standard test sequence (Figure 2). The first pop up when you start the sequence is a user guide, which can be useful unless you have customized the sequence for your own particular needs.

Figure 2: Results from the standard speaker driver test sequence.

A 1 second to 2 second sweep runs from the higher to the bottom frequency range. The device isn’t afraid of volumes as you can see in the decibel (dB) levels, the default generator setting for this test is 500 mVrms.

The overview presented is complete and extremely fast. The usual amplitude frequency response as well as the impedance curve, measured simultaneously through an extra channel in the AmpConnect unit. Additionally, you can obtain total harmonic distortion (THD) and Rub & Buzz results with the unit. Quite a complete test set from a single short sweep.

Next, let’s go into the sequence to see how we can customize it for our specific situation. We want to change the signal level and the sweep rate. We go into the sequence editor and find the Operation Flow. From the library on the left side of Figure 3, new elements can be added as needed. Each element in turn can also be customized. You cannot nest sequences, which may or may not be a disadvantage.


Figure 3: The Sequence Editor shows available functions that allow users to customize a test sequence.

Going into the signal stimulus immediately shows you the kind of software we’re dealing with here; completely flexible, where you can choose your desired templates and just drag them into the sequence (Figure 4). Double-clicking a sequence step shows the step configuration; you can change the level and range to fit a particular DUT and re-run the sequence.

Figure 4: Customizing options for the signal generator.

Within just a few minutes we have customized the test sequence, re-run the test, and are looking at the results (Figure 5 and Figure 6). All the looks and feels options are there, also simple things like scaling an axis are well implemented, just click on the values and enter the desired setting.

Figure 5: Results from the standard speaker driver test sequence after configuring ranges and limits.

Figure 6: More results from the standard speaker driver test sequence; impulse response, frequency response, TSR and harmonics.

Algorithms. This is the area where Listen presents some interesting material. You can find a lot of background on these by reading through the papers from Steve Temme, Listen’s founder and president. Just for a first impression I’ve added one older and one of the more recent analysis algorithms.

Measure Speakers in Ordinary Room Conditions. Although the Splice Near Field and Far Field Sequence implementation is relatively new, Temme wrote a paper about this principle back in 1994. The sequence contains three measurements: near-field speaker, near-field port, and far field. In the near field, the woofer and port measurements are combined into an overall response of the combination (Figure 7). Next, the far-field measurement is performed using the same stimulus (Figure 8).


Figure 7: Near-field speaker and near-field port responses combined.

Figure 8: Far-field response.

In the far-field measurement, you can see some room modes and reflections. However, these “higher” frequency modes are largely avoided by moving the microphone a bit closer to the speaker. After these measurements, the near-field response is level corrected to match the far-field response. You can enter the desired splicing frequency while looking at the two graphs after which the program will calculate the results and smoothen the curve with 1/24 octave (Figure 9). Just like the other tests we ran, it is easy to do, with results within a few minutes.

Figure 9: All three measurements can be combined in a single graph.

Enhanced Loose Particles. This new analysis (Figure 10) clearly did detect this not-well mounted speaker (the screws were left in the cabinet), while the older method (Figure 11) requires some more optimization to be able to address this. And on top of this, the precision of this measurement default is vastly improved!

Figure 10: Enhanced loose particle analysis (new method).

Figure 11: Loose particle analysis (older method).

Both the frequency response, as well as the eLP envelope, are much clearer in the newer method. On top of that, the two added graphs show some rattling around the detection of the main peak.

Software, Connectivity, Data Collection, and Reporting. The SoundCheck software is written in Labview, which also shows the connectivity and the extensive options to export and import data in or out of this system to external applications, such as MS Word and Excel, Matlab, HTML, SQL, and image formats.

SoundCheck gives you access to a memory set where the internal software variables and curves can be found. This set can be linked and used within the other functions. Importing data is a big plus here, making this software even more flexible. Some test configuration data can be passed to/from SoundCheck enabling you to store test parameters separately from the test sequences. Then the export of data provides you with all the inputs for any reports you can think of, or you can just use the provided templates to generate your reports.

AmpConnect 621 Hardware

The Interface. You obviously need an interface between the software and a DUT, and although you can use your own hardware, we used the provided AmpConnect to be able to start testing right away (Photo 2). We used this unit alongside an SCM measurement microphone and a preconditioned setup directly out of the box (Photo 3). After installing the software there are some additional steps such as calibration, however, every unit shipped by Listen comes with its own calibration values, which can be read from the software. For once it really was plug-and-play! And another plus, no fans! This interface is quiet.


Photo 2: For this test, I used the AmpConnect 621 hardware shown with the front view (a) and the back view (b).

Photo 3: The AmpConnect 621 hardware alongside an SCM measurement microphone enabled me to get started testing almost immediately.

There are no controls on the box, only some status LEDs. The reason for this is that in production environments one common test failure is that the calibration or setting of the test is accidentally changed. By having all controls and settings in the software this risk is minimized. Some representative specs and connectivity include:

6 inputs (unbalanced BNC terminals)

2 unbalanced outputs (unbalanced BNC terminals)

1 amplifier (one amplifier switchable to two outputs)

8 digital in- or outputs with Vref and Vpower (3.3V)

1 USB 2.0, with sampling rate frequencies up to 192kHz and bandwidth from 20Hz-91.2kHz

Figure 12 shows the distortion residual, which mainly consists of noise. Figure 13 shows the AmpConnect output spectrum measured with ASIO driver; D/A 192kHz/24-bit at -14dBFS -> Amplifier -> 8Ω load resistor at 2.83Vrms (1W into 8Ω). The second harmonic is at -105dB.


Figure 12: The 1kHz signal source with distortion residue is magnified by a factor of 1000.

Figure 13: This is the output spectrum at 1W into 8Ω.

This is one of the better audio test software suites I’ve worked with so far. Flexibility is the main thing here, everything is open and configurable, and even external hardware and some PC-related functions were accessible. There are many more Listen hardware options ranging from sound cards, microphone preamps to turntable devices for polar plots. The included sequencers out of the box are usable, but some will need minor adjustments mainly to match the used hardware.

The software is user-friendly, in just an afternoon you can make your first measurements while feeling comfortable with the desktop and sequences. A free set of sequences is available online (see Resources). Well done! Needless to say, I didn’t experience any breakdown or instability issues.

Hardware-wise, the AmpConnect is solid and provides for most measurements, albeit based upon unbalanced I/O. Spec-wise you can find better equipment out there, but I doubt whether that’s necessary for the intended use. The pre-calibrated delivery and the seamless cooperation with the SoundCheck software make this a proper solution for serious measuring.

We tested a full-optioned high-end set consisting of SoundCheck 21 with all the options enabled (Complete), an SCM measurement microphone set and the AmpConnect 621 interface. It’s common practice for Listen to let you use a full testing set with a time-limited license. After testing they’ll make a quote matching the required functions and hardware.

We’re not going to mention the fully elaborate pricing scheme here. You can customize everything — software is a combination of packages and modules and even the hardware is customizable. To give you just an impression of how this is structured:

Software: Most SoundCheck software packages are in the $7,000 to $14,000 range, although specialist options can push the cost higher.

Hardware: The AmpConnect 621 is a little more than $5,000, while an AudioConnect 2 would set you back around $1,600.

Microphone equipment: The SCM 4 microphone set (calibrated) is $800.

However, at any price point, you get extremely powerful and flexible functions fully calibrated and ready to go.  aX


Free Test Sequences,

Listen Announces SoundCheck Version 21 and New Portable Dual-Channel Audio Interface,“ audioXpress website, March 6, 2023,

Listen’s New AmpConnect 621 Hi-Res Multichannel Audio Interface Is Now Shipping,” audioXpress website, June 14, 2021, SoundCheck Packages and Modules, Listen, Inc.,

This article was originally published in audioXpress, March 2024

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