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Comment by bkmn | Hacker News Reader

”An Apple-designed A8 chip powers the most complex audio innovations in HomePod. Like real-time modeling of the woofer mechanics. Buffering that’s even faster than real time.”

Faster than real-time. That IS fast!

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Well, that's actually true, it can buffer the entire song and more. So it's faster than real time.

Which is not a great achievemnt with audio over WiFi really.

Were it only real-time, could you even call that buffering?

Sure. Load 10 seconds, start playing and then always have a buffer of exactly 10 seconds in memory.

But what does it have to do with the powerful cheap? Buffering is not very useful if it's slower than real time, and all that's needed for it is a connection and some memory.

"real-time modeling of the woofer mechanics" reminds me of those Philips Motional Feedback speakers [2] my parents bought in the late '70s [2]. Instead of digital "real-time modeling" they used an analog feedback loop to control and correct woofer cone movement. These were self-contained active speaker cabinets containing a 35W (later also available in 75W) amplifier and two or three speakers with the feedback mechanism controlling the woofer.

They did not have wifi or an always-on microphone, true, but the former is easily remedied (use a Raspberry Pi Zero or something similar) while the latter is more of an advantage than a disadvantage.

[1] http://www.extra.research.philips.com/hera/people/aarts/_Phi...

[2] http://hifipig.com/philips-motional-feedback-speakers/

Apple's approach goes a fair bit beyond simple servo control (which only tends to work well for truly low-frequency content.

While Apple hasn't disclosed much about the particular details, it's bound to be in the same vein as Klippel's work, which doesn't use feedback as much as it monitors a few states as input to a feed-forward error-correcting mechanism. The net result is that distortion is lower, and it's much less limited with regards to the frequency range you can support.

[1] http://www.audioxpress.com/article/louder-faithful-and-consi...

[2] https://www.klippel.de/fileadmin/_migrated/content_uploads/A...

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