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@jude what's your take on Hi-Res thing and do you think 40kHz extension matter for IEMs at all?...
@piotrus-g, I'm just trying to get meaningful headphone measurements out to 20 kHz, and haven't given this as much thought! Do I personally look for the "Hi-Res" label as part of my buying decision? No. I'm not clear on precisely how headphones are measured to 40 kHz to earn the "Hi-Res" seal -- no idea what the procedure is, how it's done. If you've had your IEMs measured for that certification, how does that work?
At the 2016 AES International Conference on Headphone Technology, Steve Temme from Listen, Inc. presented a poster covering this. From my notes and photos:
- His poster quoted David Griesinger: "The phase relationships of harmonics from a complex tone contain more information about the sound than the fundamentals."
- Temme asked, "So, why exceed 20 kHz?" His answers:
- "For a transducer to have a flat phase response out to 20 kHz, a flat magnitude out to 40 kHz is required (by definition, at resonance, there is a 90° phase shift)"
- "Inaudible high frequency components, e.g. 30 & 33 kHz resonances, can produce intermodulation products that 'beat' down into the audio band of frequencies"
- "A sampling rate of 44.1 kHz @ 16 bits adequately covers the range of human hearing and musical instruments"
- "To achieve a flat frequency response (mag & phase) out to 20 kHz requires a bandwidth beyond 20 kHz"
- "Loudspeakers and microphones that measure beyond 20 kHz can exhibit trade-offs in performance, e.g. audible intermodulation distortion"
- "Try down-sampling a hi-res audio file to CD quality and do an ABX listening comparison. Can you hear the difference?"
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