Bluetooth Headset Test Sequence

The purpose of this sequence is to test a Bluetooth headset using a mixture of analog and digital channels. First, a Multitone stimulus is created with SoundCheck, played back over the Bluetooth headset (at 8 kHz) and recorded by a head and torso simulator’s ear (at 44.1 kHz). Then the same Multitone stimulus is played back through the head and torso’s mouth simulator (at 44.1 kHz) and recorded via the Bluetooth headset (at 8 kHz).

Due to inaccuracies of clock frequency, the Bluetooth device playback sampling rate is often slightly different than it is specified. Therefore, in SoundCheck, the Recorded Time Waveforms are frequency shifted to correct for the inaccurate sampling rate. The exact device playback sampling rate is displayed.

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Headphone Test Sequence

This headphone test sequence measures a stereo headphone. Both left and right earphones are measured simultaneously using a standard 1/12th Octave stepped-sine sweep from 20 Hz to 20 kHz.

The analysis is then performed using Listen’s HarmonicTrak™ algorithm that measures harmonic distortion and fundamental frequency response simultaneously. Then the diffuse-field and free-field corrected Fundamentals are calculated. The diffuse-field correction curve compensates for the overall frequency response from the diffuse-field (sound in every direction) to the eardrum and includes the effects of the head, torso, pinna, ear-canal and ear simulator. The free-field correction curve compensates for the overall frequency response from the free-field (sound at 0 degree incidence to the nose of the Head and Torso Simulator – HATS) to the eardrum.

Further post-processing of the signal compares left and right earphone responses to show the difference curve (magnitude and phase are available). The average sensitivity from 100 to 10 kHz for both left and right earphone is calculated and the total harmonic distortion displayed.

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Amplifier THD+N Sequence

This sequence measures an audio amplifier’s Frequency Response, Gain, THD, THD+Noise, and Self-noise. It accomplishes this by playing a 1/3rd octave sine sweep through the amplifier. A HarmonicTrak™ analysis step calculates the fundamental frequency response curve as well as the distortion plots. The sequence then records and analyzes a spectrum of the amplifier’s self-noise.

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Measuring Loudspeaker Maximum Linear Sound Levels Using Noise to the AES75-2022 Standard

The AES75-2022 standard details a procedure for measuring maximum linear sound levels of a loudspeaker system or driver using a test signal called M-Noise. This is a complex procedure with many repetitive steps, which makes it time consuming to implement manually. This sequence automates the entire process, accelerating test time, minimizing operator intervention, and ensuring accurate and objective test results.

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MP3 Player (Multitone) Sequence

The principle is first to create a multitone stimulus waveform with SoundCheck and transfer it to the MP3 Player to be tested. This waveform is then played back, to be acquired and analyzed by SoundCheck. Both Left and Right channels are acquired at once. The acquisition is made easy by using a trigger on one input channel. The analysis is done by comparing the genuine stimulus and the play-back, using a cross-spectrum technique that provides the FRF, Cross-talk and Non-Coherent Distortion. The cross-talk between channels is measured by playing simultaneously two different multitones for Left and Right channels with interleaved frequencies, and making a cross-analysis between channels (e.g. finding in the right response the contribution of the left stimulus).

Due to inaccuracies of clock frequency, the play-back sampling rate is often different from the Soundcard recording sampling rate. Therefore, in SoundCheck, the recorded time Waveforms are frequency shifted as to obtain a perfect match between stimulus and responses. This frequency correction is performed on both channels before the Analysis steps. The exact playback sampling rate is displayed. The Sequence can be measure the MP3 player on the WAV or the MP3 file playback. The MP3 playback will yield a poorer FRF and more distortion, due to the lossy compression.

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Polar Plot (Linear X Turntable) Loudspeaker Sequence

This sequence measures the polar response of a loudspeaker in both the vertical and horizontal dimensions. It is designed to work with the Linear X turntable, and has all the necessary commands to automatically rotate it via RS-232. The sequence uses a log sweep stimulus with the Time Selective Response algorithm so that the measurements can be run in a non-anechoic environment. Note that the time window needs to be adapted to the user’s measurement space. The sequence plays the stimulus and measures at 10 degree increments from 0 to 180 degrees. This process is repeated with the speaker positioned horizontally. The two results are mirrored to display full 360 degree polar plots for each axis. A directivity index curve is also calculated for each axis and is displayed at the end of the test.

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Time Selective Response Sequence

This sequence demonstrates the capabilities of the TSR (Time Selective Response) algorithm in SoundCheck. Using TSR with a log sweep is a very fast and effective method for measuring frequency response and THD of a speaker in a non-anechoic environment. This example plays a quick log sweep from 20 Hz to 20 kHz. An analysis step then uses the TSR algorithm with time windowing to output frequency response, harmonics, THD, and impulse response curves.

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Enhanced Perceptual Rub & Buzz Demo Sequence

This sequence demonstrates how SC20’s new enhanced Perceptual Rub & Buzz algorithm compares to normalized Rub & Buzz and subjective listening. Running this sequence on a batch of good and bad buzzing loudspeakers should help identify by measurement, audibly defective units and where to set production limits. Starting the sequence, the user is asked at what test level to play a stepped sine sweep (Stweep™) in 1/12th octaves, from 20 kHz to 50 Hz. The user is encouraged to try different test levels and change sweep parameters to find the optimum settings to catch buzzing loudspeakers. The loudspeaker is measured via two channels of the audio interface. A calibrated reference microphone is connected to one of the channels and an impedance reference built into the SC Amp or AmpConnect is connected to the other. A HarmonicTrak™ Analysis step analyzes the recorded waveform from the reference microphone, and displays both the enhanced Perceptual Rub & Buzz and normalized Rub & Buzz graphs.

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Complete End-of-Line Speaker Test (includes ePRB and eLP)

This sequence is an example of the many types of tests that can be performed quickly and simultaneously on a loudspeaker production line. A stepped sine sweep (StweepTM) from 20 kHz to 50 Hz is played through the speaker under test and measured via two channels of the audio interface. A calibrated reference microphone is connected to one of the channels and an impedance reference built into the SC Amp or AmpConnect is connected to the other. A HarmonicTrak™ Analysis step analyzes the recorded waveform from the reference microphone and outputs Frequency Response, THD, Normalized Rub & Buzz, Perceptual Rub & Buzz (ePRB), Loose Particle Prominence and Threshold (eLP) and Polarity. A Post-Processing step calculates the Average Sensitivity from 100 – 10kHz. A second Analysis step analyzes the recorded waveform from the impedance reference and outputs a curve of impedance versus frequency. A Post Processing step performs a curve fit of the impedance curve and calculates the max impedance (Zmax), precise resonance frequency (f0), and the quality factor (Q) of the resonance peak. All measurements and parameters are tested against limits in Limit steps. All these limits can be adjusted to suit your own DUT.

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Measuring Hearing Protection Devices to ANSI S3.19-1974 Standard

This sequence is used to measure the NRR, or Noise Reduction Rating, of a hearing protection device to the ANSI S3.19-1974 standard. NRR is a numerical representation of the sound attenuation of a device. The sequence first measures the response spectrum of the unoccluded hearing protector test fixture, then makes a second measurement with the hearing protection DUT affixed. A signal generator virtual instrument generates the pink noise stimulus while an RTA virtual instrument simultaneously records the A and C weighted noise spectrums. The unoccluded and occluded measurements are analyzed with a series of post-processing steps according to the ANSI S3.19-1974 standard. The final display shows the NRR numerical value, RTA spectra of the left and right side of the unoccluded and occluded hearing test fixture, average attenuation level of the DUT, and the standard deviation of the DUT on the test fixture.

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