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Korea Headphone Seminar

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Over 150 people attended the Listen, Inc./G.R.A.S. headphone seminar in Seoul on Tuesday March 6th, where Steve Temme, Peter Wulf-Andersen, Dr. Sean Olive and Prof. Lee spoke to a packed room about headphone measurement, perception and design and tuning. It was a great event and exciting to meet so many of Korea’s top audio design engineers. Thank you for coming! And of course a huge thank you to our very special guest speakers, Dr. Olive and Prof. Lee.

Videos of the event (in English and Korean) can be viewed using the links below (videos will open in a new tab).

Peter Wulf-Andersen – G.R.A.S.: https://youtu.be/sTZpShVDaoI

Steve Temme – Listen, Inc.: https://youtu.be/35TtshAENdo

Prof. Lee – New Media Communication Joint Institute of Seoul National University: https://youtu.be/mhLW03PvLmw

Dr. Sean Olive, Harman International: https://youtu.be/B8cNf0Q3tNs

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Bluetooth Headset Measurement

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This sequence tests 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 Test)

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open_loop_headphone_screenshotThis sequence tests a stereo headphone connected to a portable audio device such as a mobile phone or MP3 player. It 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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