Tag Archive for: headphone

100 Things #81: Using Statistics to Overcome Fit Variation for Headset Measurements

SoundCheck’s statistics allows for multiple measurements from a sequence to be analyzed together, to determine results like average and standard deviation. Using statistics can overcome placement variations when measuring headsets on a head and torso simulator. This sequence demonstrates a measurement of a USB headset, performed five times, where the headset is removed and repositioned on the HATS each time. SoundCheck’s statistics then take these five measurements, account for the differences in placement, and display an accurate set of measurement results. If you are testing to standards then statistics makes measurement of communications devices fast and repeatable.

Using Statistics to Overcome Fit Variation for Headset Measurements

Try measurement statistics in SoundCheck

Learn more about our pre-written TIA-920-B test sequence mentioned in this video. This pre-written sequence tests to TIA 920-B, a comprehensive US dual-bandwidth standard that applies to both narrowband (NB) and wideband (WB) devices.

Video Script:

Statistics have been a feature in SoundCheck for a very long time. But did you know that statistics can be used to overcome fit variation when measuring body-worn devices? Let’s look at how we can use this feature to make repeatable TIA-920B measurements on headsets?

For realistic and accurate results, headsets and other body-worn devices should be measured on a Head And Torso Simulator, or HATS, placed just as worn by real users. Unfortunately, small changes in position can lead to significant changes in both the level and the sound quality, whether on a real person or HATS.

For example, when placed carefully, the receiver of our USB headset sounds like this. (Audio example 1: proper placement)

When placed poorly, it sounds like this. (Audio example 2: improper placement)

To obtain repeatable results, we make several measurements and average the results, using the Statistics Step.

The headset is completely removed from HATS after each measurement, then repositioned for the next. With practice, 5 measurements are usually enough. This procedure is defined in ITU-T P.380 and IEEE 269 and used in Listen’s pre-written sequences that implement TIA 920-B.

Let’s make some measurements.

We are testing a USB headset that has two receivers and a boom microphone, intended for speech communication. There may be some speech-sensitive signal processing, so the test uses real speech. The signal is played out to the receivers first, then to the HATS mouth.

When the first measurement is finished, the receive frequency responses and single parameters such as output level are shown on the top line

In a similar way, the sidetone frequency responses are on the second line, and the send frequency response is on the bottom line.

After 5 measurements, with re-positioning between each measurement, we can see the individual frequency responses. Let’s take a closer look at the Left receive frequency response. The individual frequency responses are in gray, the current measurement in white, and the current mean in blue.

After the last of the measurements, we can see the mean results. Tolerances from the standard have been applied to the mean receive and mean send frequency responses.

The standard deviations show the repeatability of the individual measurements. If the standard deviations are within the tolerances, the mean results are acceptable. When results from 2 or more operators using this method are compared, the mean results will usually be very close, even if the individual measurements are somewhat different.

Statistics helps overcome fit variation to make accurate and repeatable measurements of headsets, as well as most other body-worn devices such as helmets, goggles, parrots and so on. And, if you are making TIA-920-B measurements on such devices, you can save a lot of test writing time with our pre-written TIA-920-B sequences. These can be used for USB, Bluetooth or wired analog devices, and there are also open-loop sequences for testing devices that connect to a server.

100 Things #57: Measuring Headphone Active Noise Cancellation in Real Time

Active Noise Cancellation technology is more advanced than ever, and SoundCheck is well-equipped with all the features needed for measuring headphone active noise cancellation. We have a pre-written test sequence to measure all aspects of noise cancellation including passive, active, and total noise attenuation. This sequence is a great fully complete test, or you can use it as a template to expand your test setup to include multiple background noise sources, or add an additional microphone for an even more detailed test of how the ANC circuit responds to dynamic signals.

Measuring Headphone Active Noise Cancellation in Real Time

Try ANC headphone measurements for yourself

Find our free sequence for measuring Noise-Cancelling Headphones here. This sequence first measures the passive attenuation of the headphones, then the active attenuation, and finally calculates the total attenuation.

Video Script:

Did you know you can measure headphone Active Noise Cancellation with SoundCheck, as well as standard acoustic tests such as frequency response and distortion? When measuring noise canceling headphones there are three important measurements to make: passive attenuation, active attenuation, and total attenuation. Passive Attenuation is the amount of noise the headphones block without ANC enabled. Active Attenuation is the amount of noise ANC blocks out. Total Attenuation is the combination of the two measurements.

We even have a pre-written sequence showing off this functionality, called Noise Canceling Headphones, available on our website. You will need a Head and Torso Simulator (HATS) or an acoustic ear simulator with an artificial pinna, at least one speaker for background noise generation, and a set of headphones with ANC.

The first measurement is taken without headphones on the HATS, the unoccluded measurement. The pink noise stimulus is played out of the speakers, and the signal from the HATS is recorded. Next, the sequence pauses while the operator places the headphones on the HATS, then makes the occluded measurement. The sequence again pauses for the operator to enable the headphone’s active noise cancellation, and The third measurement is taken, and the results are calculated.

This test can be modified to work with a diffuse, multi-speaker configuration, and in an environment with two or more speakers, both ears could be measured at the same time. Our new AmpConnect 621 interface has six inputs, and two outputs so you can even measure both the left and right channel simultaneously, while also generating stereo background noise. Using SoundCheck’s new Multichannel RTA, you can measure the acoustic seal  of both the left and right headphone channels simultaneously, and even visualize it in real time. Also, with the Multi-RTA and an external reference measurement microphone positioned immediately next to the outside of the headphone, you can play any complex signal you like out of the source speaker(s) such as real recorded background noise from an airplane and watch in real time how the noise attenuation changes. This is a more realistic representation of how the ANC circuit responds to dynamic signals.  

There are many ways you can modify this sequence, for example, instead of playing out of one source speaker, play out of multiple equalized source speakers to create a more realistic spatial background noise environment. With the new Signal generator’s delay offset feature, this is much easier to do.

How do you measure active noise cancellation? And what are your favorite noise-canceling headphones? Let us know in the comments below! And for more information on all things SoundCheck, head to our website at ListenInc.com.

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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Prediction of Listener Preference of In-Ear Headphones (Harman Model)

This sequence, inspired by AES papers on statistical models to predict listener preference by Sean E. Olive, Todd Welti, and Omid Khonsaripour of Harman International, applies the Harman target curve for in-ear, on-ear and over-ear headphones to a measurement made in SoundCheck to yield the predicted user preference for the device under test. The measurements are made in SoundCheck and then saved to an Excel template which performs the necessary calculations to produce a Predicted Preference score using a scale of 0 to 100. The spreadsheet calculates an Error curve which is derived from subtracting the target curve from an average of the headphone left/right response. The standard deviation, slope and average of the Error curve are calculated and used to calculate the predicted preference score. The sequence also provides the option to recall data rather than making a measurement, which saves time for engineers who already have large quantities of saved data, and enables historical comparison with obsolete products.

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Bluetooth Headset Testing

Screenshot of final SoundCheck display of Bluetooth Headset Testing Sequence

Final display of Bluetooth Headset Testing Sequence

This Bluetooth Headset testing sequence for SoundCheck measures the send and receive performance of a stereo Bluetooth headset with a built-in microphone using a mixture of analog and digital channels. The left and right earphones are measured simultaneously with a stepped sweep from 20kHz to 20 Hz using two Bluetooth profiles: A2DP and HFP. The mic is measured with a stepped sweep from 8kHz to 100Hz using the HFP profile.

A short 1kHz tone is pre-pended to the test stimulus which serves as a reference tone for resampling and frequency shift operations. Post-processing resampling and frequency shift precisely synchronizes the stimulus and response waveforms prior to analysis. In this case, the HarmonicTrak algorithm is used for frequency and THD analysis. A2DP frequency response and THD curves are displayed on the first display, followed by A2DP & HFP curves superimposed on a subsequent display. Lastly, the Bluetooth headset’s microphone is tested with HFP and its frequency response is shown on the final display along with the previously collected data.

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Lightning Headphone Test (Open Loop Headphone Test)

open_loop_headphone_screenshotThis sequence tests a stereo headphone connected to a portable audio device such as a mobile phone or MP3 player. This open loop headphone test is particularly useful for testing headphones with proprietary connectors such as the Lightning connector which otherwise can’t be tested in a conventional “closed loop” test configuration.

The test stimulus is created in SoundCheck, saved as a WAV file and loaded on to the portable device for playback. Both left and right earphones are measured simultaneously using a continuous log sweep from 20 Hz to 20 kHz. The sequence uses a short 1 kHz tone, pre-pended to the normal test stimulus to automatically trigger the test when playback of the test signal begins; it also serves as reference tone for any frequency shift calculations. Post-processing precisely synchronizes the stimulus and response waveforms, and then calculation of the measurement parameters proceeds as with any conventional headphone. In this case, analysis is performed using the Time Selective Response (TSR) algorithm which performs THD and fundamental frequency response analysis simultaneously in addition to producing an impulse response. The fundamentals are then post processed to derive the sensitivity of the left and right channels at 1 kHz.

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