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

[Jay Schwichtenberg]

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.

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.
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.
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.

Jay

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of James Patchell
> Sent: Monday, January 05, 2004 9:42 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Taking a Step towards Digital Synthesis?....
>
>
>          Well, today I did it, I ordered the Memec DS-KIT-3SLC400-BAS
> Xilinx Spartan 3 Eval board (it comes with an XC3S400 chip, USB,
> RS232 and
> JTAG ports).  The real reason is actually to work on a motion controller
> design, but, I figured I could also spend some time implementing
> a digital
> synthesizer in there as well :-)  Delivery time is about 3 weeks from now
> :-(  ... but I figure I can survive the wait.
>
> The XC3S400 has about 300K bits (36K bytes) of block ram and 16 18x18
> multipliers (I can't believe the multiplier count, I can remember when a
> 16x16 multiplier chip was a very expensive item).
>
> I need to start looking about for some 24 bit audio dacs now for
> doing the
> digital synth...errr...I mean motion controller.... :-)
>
>
>          -Jim
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> I'm a man
> But I can change
> If I have to
> I guess.
>
> Man's Prayer
> Red Green
>
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>
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