100 Things #89: Apply Equalization To A Test Stimulus

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.

Video Script:

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.