[Fpga-synth] phLUTe

[Scott Gravenhorst]

Eric Brombaugh <ebrombaugh at earthlink.net> wrote:
>Scott Gravenhorst wrote:
>> I'm actually thinking of buying a protoboard to stick on a better DAC
>
>
>Might I suggest the following:
>
>CS4344
>UDA1334
>
>I2S Stereo Audio DACs with sample rates up to 100kHz. Cost < $2 in 
>single quantity. Code to drive them is simple. Only downside is that 
>they're SMD, but using DIP/SMD adapters works OK.

I must say that I've been spoiled by the high sample rate of the 12 bit on board DAC.  

I see that there are some DACs, 16 bit that run at 192KHz sample rate.  The ones I saw
(Mouser cat) were < $4.  I'd like to have a just a tad more headroom than 100KHz for
the use of state variable filters which don't appreciate signals more than about 1/6
of the sample rate.  I believe these DACs are made by TI.  ??  

I really know very little about DACs - what types should I absolutely avoid?


>> and I thought I might throw some SRAM at it at the same time.
>
>Not a bad idea.
>
>> It seems to
>> me that the sharing will prevent using the DAC at high sample 
>rates - and I love high sample > rates because they allow you to 
>do things like these simple interpolaters for tuning as well as > 
>state variable filters. 
>
>Depends on what you mean by 'high sample rates'. I've got a bank of 
>oscillators running at ~1.6MHz sample rate each. I sum them together and 
>then decimate down to 48kHz. This allows sharing the math hardware and 
>still using a low-cost, high-quality audio DAC. The trick is coming up 
>with a good decimator to bring you down from the 1.6MHz rate to 48kHz 
>without aliasing.

I was referring more to the fun clocking required for the SDRAM and then trying to use
the onboard DAC at the same time.  The DAC can run at 1.0 MHz, but at that rate,
sharing the SPI pins with the SDRAM would be impossible because the DAC would
monopolize the SPI lines at that speed.  Thus to use the DAC, it would have to run at
some rate less than 1.0 MHz.  I haven't tried to figure out how fast it will go - does
anyone already know what the max DAC sample rate would be when used in conjunction
with the SDRAM?  That whole nightmare is why I want an offboard DAC...

-- ScottG

-----------------------------------------------------------------

-- Scott Gravenhorst
-- GateMan-III - FPGA Based Monophonic MIDI Synthesizer with SVF
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