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Practical Testing of Voice Controlled Devices

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Author: Steve Temme.  Reprinted from the Jan 2020 issue of AudioXpress.

This article discusses tools and techniques that are available to accurately measure the audio performance of voice-controlled and connected devices under the many various real-world conditions they may be used. It covers basic acoustic measurements such as frequency and distortion response, which have always been carried out on conventional wired systems, and the more complex real-world tests that apply specifically to voice-activated devices, along withthe techniques and standards that may be used.
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Microphone SNR Measurement (Background Noise Method)

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This sequence characterizes a microphone’s ability to passively and/or actively reject noise in the user’s environment.  Unlike traditional microphone SNR measurements which calculate a ratio based upon a reference signal and the microphone’s noise floor, this method utilizes a signal (speech played from a mouth simulator) and noise (background noise played from two or more equalized source speakers) captured by both a reference microphone and the DUT microphone.

First a recording of the baseline ambient noise in the test environment is made and a 1/3 octave RTA spectrum is calculated from the recording. Next, the speech signal (mouth simulator) and noise signals (Left and Right speakers) are played consecutively and recorded separately using the reference microphone. A 1/3 octave RTA spectrum is calculated from each recorded time waveform. Next the same measurements are repeated using the DUT microphone. The resulting RTA spectra are then post processed to produce a signal gain spectrum and a noise gain spectrum which are then used to derive the SNR spectrum of the DUT mic. For best accuracy, the Signal and Noise spectra should be at least 5 dB above the ambient noise floor of the measurement environment.

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Listen offers ETSI Standard background noise generation system

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Listen offers ETSI Standard background noise generation system

Listen, Inc. has launched the ETSI standard background noise generation module, a SoundCheck test sequence which calibrates a 4.1 speaker array to conform with the ETSI ES 202 396-1 Standard. This provides an equalized, calibrated playback solution to stress devices in a standardized and repeatable way. The sequence includes a library of real-world binaural recordings from the ETSI standard: cafeteria, pub, crossroad, vehicle, single voice distractor, and office noises.  Custom or user-defined binaural recordings can also be used. With a purchase price of just $5,000 for the test sequence, this offers an extremely economical alternative to a conventional $20,000+ stand-alone background noise generation system.

Furthermore, it offers the advantage that the ETSI standard library is fully integrated with, and managed by, the SoundCheck test system. This means that the calibrated background noise levels can be fully controlled and adjusted as part of a pre-programmed test sequence, significantly reducing test development time as well as simplifying the physical setup.

This has many applications, for example evaluating ANC, noise suppression, SNR optimization of microphone arrays, beamforming directionality studies, and more. It is particularly useful for voice recognition testing as the test sequence may include loops to incrementally increase the volume or change the noise and repeat the test until the voice is no longer accurately recognized.

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Background Noise Simulation to ETSI ES 202 396-1 Standard

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Background_noise_simulation_screenshotThis Background Noise Simulation sequence follows the ETSI ES 202 396-1 standard.  It will automatically calibrate a standardized 4.1 speaker / subwoofer setup in accordance to the ETSI ES 202 396-1 standard “Loudspeaker Setup for Background Noise Simulation” and provide an equalized, calibrated playback solution to stress your device in a standardized and repeatable way.

Included with the sequence is a library of real world binaural recordings from the ETSI standard: cafeteria, pub, crossroad, vehicle, single voice distractor, and office noises.  Custom or user-defined  binaural recordings can also be used to create background noise tests directly applicable to your product. This sequence has many applications including evaluating ANC on headphones, noise  suppression on communication devices, voice recognition testing of smart speakers / IoT, SNR optimization of microphones on telepresence devices and beamforming directionality studies of microphone arrays.

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