Frequency-Normalized THD Test Sequence

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This sequence measures both conventional Total Harmonic Distortion (THD) and Normalized THD to provide a more accurate representation of a device’s nonlinear behavior. A stimulus is played through the device under test and recorded via a calibrated reference microphone and amplifier signal paths. Conventional THD compares each harmonic to the fundamental at the stimulus frequency, which can cause distortion results to be influenced by the device’s frequency response roll-off. Normalized THD instead compares each harmonic to the fundamental at its measured frequency before plotting the result at the stimulus frequency, removing the effect of linear response variations. Both methods can be displayed and analyzed within the same step, allowing direct comparison of traditional and normalized distortion results.

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Smart Glasses Speaker Output Test Sequence

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This sequence measures the frequency response, THD, and L/R balance of Bluetooth smart glasses speakers. After pairing the device with the BQC-4149 and placing it on a HATS, a 1 kHz pilot tone with a 20 kHz–100 Hz Stweep stimulus is played and captured through the ear simulators. The HarmonicTrak algorithm then analyzes the recording to display output performance.

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Smart Glasses Mic Input Test Sequence

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This sequence measures the frequency response of Bluetooth smart glasses microphones. After pairing the device with the BQC-4149 and mounting it on a HATS, a stimulus is played through the mouth simulator and recorded by the microphone. The HarmonicTrak algorithm then analyzes the recording to display the fundamental frequency response.

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Triggered Record Using Chirp Trigger and WAV File (Version 17 and later)

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This test sequence demonstrates SoundCheck’s Triggered Record – Chirp Trigger function for open loop testing of devices without analog inputs such as smart speakers, wearables, smart home devices, tablets and cellphones.  A stimulus WAV file is created in SoundCheck and transferred to the device under test, where it is played back and the response recorded in SoundCheck as if the stimulus were played directly from SoundCheck. The Acquisition step is triggered by the chirp in the stimulus file. Chirp triggers are more robust than level and frequency triggers which are susceptible to false triggering due to background noise.

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Smart Speaker Embedded Microphone Test Sequence

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smart_speaker_final_display_micThis sequence demonstrates a method by which SoundCheck can measure the performance of a microphone embedded in a so-called “smart speaker.” This smart speaker embedded microphone test assumes that the DUT is an Amazon Echo, but it can be adapted for use with virtually any other type of smart speaker by substituting the Echo’s voice activation phrase WAV file (“Alexa”) with one specific to the desired make and model.

The sequence begins by playing a voice activation phrase out of a source speaker, prompting the DUT to record both the voice command and the ensuing stepped sine sweep stimulus. A message step then prompts the operator to retrieve this recording from the DUT’s cloud storage system. This is accomplished by playing back the recording from the cloud and capturing it with a Triggered Record step in the SoundCheck test sequence.  The Recorded Time Waveform is then windowed (to remove the voice command) and frequency shifted prior to analysis and the result (Frequency Response) is shown on the final display step.

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Smart Speaker – Embedded Loudspeaker Test Sequence

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smart_speaker_final_displayThis sequence demonstrates a method by which SoundCheck can measure the performance of a loudspeaker embedded in a so-called “smart speaker”. This example assumes that the DUT is an Amazon Echo but it can be adapted for use with virtually any other type of smart speaker by substituting the Echo’s voice activation phrase audio file (“Alexa, play Test Signal One”) with one specific to the desired make and model.

The sequence begins by playing the voice activation phrase out of a source speaker, prompting the DUT to playback the mp3 stimulus file from the cloud, followed by a pause step to account for any activation latency. Following the pause, a triggered record step is used to capture the playback from the DUT. The Recorded Time Waveform is then frequency shifted prior to analysis and the results (Frequency Response, THD and Perceptual Rub & Buzz) are shown on the final display step.

We recommend reading our AES paper on this subject prior to continuing as it contains additional details on the test methods devised for this sequence.

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Open Loop Microphone Test

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Open loop microphone test

This sequence demonstrates the two most common microphone measurements, frequency response and sensitivity, on a microphone embedded in a recording device. Typically, when measuring a microphone, the response of the device can be captured simultaneously with the stimulus. However, with devices such as voice recorders and wireless telephones, forming a closed loop can be cumbersome or impossible. This sequence demonstrates how to perform an open loop microphone test by recording the signal on the device under test, transferring that recording to the computer running SoundCheck, and then using a Recall step to import the recorded waveform and analyze it.

This specific sequence, v4, is an improvement on the prior versions. The v1 release required that the audio file containing the recorded response waveform be manually windowed outside of SoundCheck before being analyzed. The v2 release utilized a new feature in SoundCheck 14, using values from the memory list to semi-automatically trim the waveform before analysis. The v3 release completely automated waveform editing through the use of an intersection level and windowing post processing steps. Currently the v4 release uses the new Auto Delay+ algorithm, exclusive to SC18 and beyond. Auto Delay+ is capable of detecting and accounting for delays of -0.5 seconds to any positive delay, nullifying the need for windowing steps in the sequence. If you are interested in learning more about this algorithm please refer to the Analysis section of the SoundCheck manual.

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ABOUT LISTEN INC

Listen is a global leader in audio measurement and analysis, with over 30 years’ experience developing innovative test methods and algorithms. SoundCheck, our powerful software-based audio analyzer, pairs with our test interfaces, precision microphones, and accessories to offer a complete solution for testing loudspeakers, headphones, microphones, smart devices, communication systems, hearing aids, automotive audio, and more. Trusted by engineers worldwide, Listen delivers the accuracy and flexibility essential for modern audio testing, from the R&D lab to the production line.

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