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100 Things #89: Apply Equalization To A Test Stimulus

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Did you know you can equalize a stimulus in SoundCheck to remove the influence of hardware and components from your measurements? All of SoundCheck’s stimulus options can have EQ applied, include Stweep, waveforms, noise, and more. An EQ can also adjust a stimulus to focus on different frequencies, like boosting low or high frequencies for power testing. THD+N measurements benefit from this ability, as even applying a flat EQ curve to a Stweep smooths out frequency transitions.

Apply Equalization To A Test Stimulus

Learn more about SoundCheck stimulus flexibility

The stimulus is just one part of the completely flexible SoundCheck system. Learn more about SoundCheck’s features and applications.

If you want to try for yourself, our SoundCheck sequence library includes applications from measuring loudspeakers to microphones, VR headsets to cars, and more. Each sequence uses a stimulus configured to the device under test, and recommended hardware.

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Did you know you can equalize any stimulus inside SoundCheck during its playback? In any test application, it is important to ensure that the inherent characteristics of the measurement hardware do not influence the measurement. For example, if you’re using a source speaker to measure a DUT microphone, you don’t want the loudspeaker’s frequency response to influence the measurement. You may also want to apply your own custom EQ curve to weight certain frequencies different, for example, boost low frequencies more than higher frequencies for power testing. You can import whatever EQ you prefer.

We can also equalize the source speaker using a reference microphone. First, we measure the speaker’s response, then invert it to give us the EQ curve. This curve can then be applied to any stimulus playing through the source speaker to correct for both magnitude and phase non-linearities.

When you check the ‘Apply EQ’ checkbox in SoundCheck’s stimulus step, the EQ curve is applied to the stimulus and saved to the memory list, ready for playback during the acquisition step.

This feature is available for all stimulus step types. For step-based stimuli such as Stweep and Multitone, where the stimulus doesn’t have all frequency components, EQ is applied only at those frequency points that are present. For Broadband stimuli like speech, music and Noise, ‘Apply EQ’ behaves like a time waveform filter.

There’s also another reason why you might want to use EQ in a step based stimulus such as a Stweep. When EQ is applied, even if there is no EQ curve, the transition from frequency step to frequency step is smoothed. This is particularly helpful for measurements such as THD+N, which are sensitive to ringing.

Naturally, ‘Apply EQ’ can be turned off if you want to characterize the speaker itself.

SoundCheck’s stimulus step provides many advanced options for a wide range of use cases. To learn more, check out our website or speak to your local sales engineer.

100 Things #14: Compound Stimuli Offer Complete Test Flexibility

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Sometimes a simple stimulus is not enough for your testing application. Maybe you need a stweep to test the range of your speaker, but also need to warm up the driver with pink noise. Or, maybe you are testing smart devices that require a wake word prior to recording. Perhaps you want to decrease testing time by using a lower resolution stweep at lower frequencies, while still retaining a higher resolution stweep for increased measurement accuracy in the higher frequency range. No matter your specific needs, SoundCheck’s stimulus editor allows users to create even the most complex compound stimulus with ease.

Compound Stimuli Offer Complete Test Flexibility

Testing smart devices with a compound stimulus

Compound stimuli are a great way to test smart devices, smartphones, or any device that requires a wake word for operation. By appending a stimulus with a wake word, the device can become active and record the test signal, allowing for automated smart device tests. Check out testing smart devices with a compound stimulus in our Smart Device Testing Seminar.

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SoundCheck allows you to build a custom stimulus consisting of as many different components as you need. You have full control over which parts of the stimulus are analyzed, so it’s easy to vary the stimulus across the test frequency range or use conditioning signals and wake words that are eliminated from the analyses.

One common application of a compound stimulus is to optimize a test signal for high accuracy and short test time. For example, when testing a loudspeaker ⅓ octave resolution can be used to sweep through the low frequencies quickly, and then 1/12 octave resolution is used at the higher frequencies to maintain measurement accuracy.

There are also many applications where it’s useful to use a conditioning tone followed by the test stimulus.

One use-case is to play a conditioning signal to warm up a speaker before a Stweep test signal is played. In this case, only the Stweep part of the signal is analyzed.

Another common application is to use the tone as a frequency trigger for triggered record acquisition, used in open loop measurements. When testing devices such as smart speakers, the stimulus is often prepended by a sinewave pilot tone, or even a chirp-based conditioning tone. These are not analyzed, but rather used to align the stimulus and response signals for analysis.

We might also use a frequency peak as a reference for performing frequency shift post-processing.

In telecoms tests, a conditioning signal may be used to trigger a voice activity detector before playing the signal for analysis. In some cases, a modulation segment may also be added to the tone. 

When testing voice activated devices, a compound stimulus allows a wake word to easily be prepended to any command or test signal.

These are just a few examples – what compound stimulus would you create with SoundCheck?  The possibilities are endless.

100 Things #5: Test Devices Using Speech or Music

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SoundCheck can test devices using any .wav file as a stimulus. This enables real signals such as speech or music to be used in any audio test. Speech signals are used for telephony and voice activation and in testing to IEEE and ITU standards that use P50 speech and ITU Real speech recordings. These ‘real world’ test signals are also valuable for measuring devices that include nonlinear signal processing such as cell phones and hearing aids, as these often do not test accurately with sine waves.

Test Devices Using Speech or Music

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Read on about all of SoundCheck‘s stimulus options and more, with features perfect for R&D and Production.

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SoundCheck can test devices using any .wav file as a stimulus. This functionality, available since 2004, enables real signals such as speech or music to be used in any audio test. Speech signals are used for telephony and voice activation and in testing to IEEE and ITU standards that use P50 speech and ITU Real speech recordings. These ‘real world’ test signals are also valuable for measuring devices that include nonlinear signal processing such as cell phones and hearing aids, as these often do not test accurately with sine waves.

Testing devices using music as a stimulus enables measurements, such as non-coherent distortion, to be made with test signals that simulate the product-use, returning results that correlate well to listener experience.

The use of wav files also means that in the rare case you want to use a custom signal that cannot be created using SoundCheck’s stimulus editor, it can be made in another program and imported as a WAV file for use in SoundCheck.

All Wav files can, of course, be calibrated and equalized in SoundCheck, ensuring reproducibility and compliance to standards.

More recently, in 2019, we added the capability for SoundCheck to open multichannel WAV files into the memory list, signal generator and stimulus steps. This enhances the testing of smart devices and microphone arrays, conveniently auto-naming and grouping the channels together.

So there you have it, wav files introduce the ultimate in flexibility to your test stimuli.

Stimulus Tutorials

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This series of 9 short tutorials explains the various stimuli available in SoundCheck, discussing when you might use them and how to configure them in SoundCheck.

Part 1 – SoundCheck Stimulus Basics
Part 2 – Advanced functions of the Stimulus Editor
Part 3 – Frequency Stepped Sweep (Stweep)
Part 4 – Frequency Log Sweep Stimulus
Part 5 – Amplitude Log Sweep Stimulus
Part 6 – Wav file Stimulus
Part 7 – Two-tone Stimulus
Part 8 – Noise Stimulus
Part 9 – Multitone Stimulus

Audio Test Stimuli – An Overview

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Stweep Stepped Sine Wave Stimulus

Stweep Stepped Sine Wave Stimulus

Author: Steve Temme

Most audio analysis systems offer a wide range of stimulus option, and selecting the right one can be daunting. This overview explains the different stimulus types, what the waveforms look and sound like (click the speaker icon to hear the sound), the advantages and disadvantages of each and when you would be likely to select each one.

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Stimulus and Acquisition

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An overview of how to use the various stimuli in SoundCheck including the stimulus types, parameter configuration, and implementation via acquisition steps. Presented by Brian Fallon, Listen, Inc. Status: Recorded. Watch Webinar