Proper Digital Audio Playback

The PonoPlayer got it right, whether they survive as a business or not.

There is a right way and a quick way to build a digital audio playback circuit.

The following information comes from Charlie Hansen, the designer of the Pono audio chain, and the excellent review by Tyll Hertsens. I’m putting it into it’s own post so other audio device builders get inspired.

  • EVERYTHING from DAC to jacks is DC coupled. No coupling caps anywhere.
  • Everything is TRULY balanced from the DAC chip all the way to the output jacks. There is no virtual ground needed, as we have true +/- rails from the switching power supply. The raw rails go to SUPER low noise regulators, of which there are a TON.
  • The audio circuitry has their own dedicated +/- regulators.
  • All of the digital circuitry runs off of positive voltage only
  • Three or four separate dedicated regulators there — one for the audio master clocks, another for the digital side of the DAC chip and a third for the rest of the digital circuitry.

“NOBODY builds portable players that are fully-discrete, fully-balanced, and zero-feedback. This all makes a huge difference.”

— Charlie Hanson of Ayre Audio

That’s what happens after the DAC, in the analog stage.



Regarding the file quality and DAC behavior before the analog stage, we have more details from Charlie:

 

  • Brickwall filtering creates massive time smear.
  • The human ear/brain is already known to be exquisitely sensitive to time smear.
  • DBT and AB/X are really only sensitive to differences in frequency response. Using these tools for anything to do with music is like pounding a nail with a screwdriver. Ain’t gonna work.

Specifically, one of the massive benefits of a higher sampling rate is not extended bandwidth.

Instead, it allows for gentler filters to be used.


In the case of the Ayre QA-9 A/D converter, the anti-aliasing filters have zero ringing or time smear for double and quad sample rates. (Only one cycle of ringing for single rates — something has to give somewhere…)

When Ayre designed the PonoPlayer’s audio circuitry, we held back nothing.

We gave it everything that could fit within the constraints of the budget, physical space, and battery life.

Every single secret we discovered went into the PonoPlayer. The digital filter is taken directly from our own products.