[sdiy] Taking a Step towards Digital Synthesis?....

[Colin Hinz]

On Tue, 6 Jan 2004, Jay Schwichtenberg wrote:

> Jim,
>
> Here are a few suggestions on picking a DAC and working with digital audio.
> Stuff I figured out after doing 4 cards. The major players in the field are:
> Crystal, AKM, Burr Brown/TI and Analog Devices.

How do the Philips parts compare to the "big players" out there? I ask
as the UDA1355H sure seems like a neato part -- not just analog CODEC
functions, but S/PDIF I/O as well. Lots of strange internal routing
possibilities, too, for those with a microcontroller handy to fly
the thing.

> 1) Use multibit converters. These are more tolerent of clocking issues and
> sound better.
> 2) PC layout is super critical. Crosstalk, power supply and grounding are
> all issues. Read all the app notes on this from all the venders.
> 3) Power supply is critical. Most chips run off of 5 and 3.3 volts. Make
> sure you have a clean and stable power supply.
> 4) Clocking is less critical with multibit converters up to a point. Try to
> get them as good as you can. Use a clock that is an exact multiple of your
> sample freq or one of the digital audio clock chips.

How do the codecs with integrated clock synthesis shape up? Again, I
refer to the UDA1355H, which specifies a fixed 12.288 MHz crystal
regardless of the analog sampling frequency. Yes, there's an internal
PLL, but they're pretty pervasive these days.....

> 5) Use a 256X or 512X master clock. Some converters don't support 384X, but
> all support 256X and most 512X. This will give you more options if you want
> to change down the road.
> 6) Do the math on the output filters yourself. Don't rely on the data sheets
> and app notes. Some of them are in error.

Rhetorical question: the datasheet claims that "on-chip filters take
care of it all" are not to be trusted, then?

> 7) Some AKM converters have a nasty thump on power up when internal caps
> charge. This requires special circuitry if you want to get rid of it.
> 8) If you can try to put a SPDIF interface in. More and more stuff is going
> this way. There are chips from Crystal and AKM that you should be able to
> put in parallel with the DAC. If you want to go hard core you can put in
> word or external sync also.

S/PDIF is almost free....may as well have it if you can get it :=)

BTW, I'm coming at this pretty new, relatively speaking - translated:
whereas I know audio a thousand times better than the average PC gamer
lamer, I bow to the more experienced minds on the list. I hope to learn
much more than I already know.

- Colin Hinz
  Toronto, Canada