I would love to get that chip.. but here in Malaysia, i dun think that chip is easily obtainable.. I may have to order it from overseas.. US$2 is equivalent to $7 and that is excluding the shipment cost.. Shipment itself is maybe $10 to $20 more so eventhough the chip is cheap, but the total cost is alot more expensive..Oznog said:Still saying this sounds way more difficult than it needs to be.
dsPIC33F will do 40MIPs, and its 16-bit instruction set and DSP core is way more efficient per instruction. So if you need power that is it.
An Si3000 codec is pretty much stock. That's like $2. It'll be a microphone preamp, software adjustable, and a headset amp (although it's a pretty weak one actually). Maxim-IC's "DirectDrive" is the BEST headphone driver, they have codecs which have it and they have basic analog amp chips with it.
DirectDrive is where they use a charge pump to make a -Vdd and it's got an output that swings close to the rails with a high current capability. Then you can hook up a speaker without having to use differential mode OR large coupling caps and you still get +/- Vdd swing off of even 3.3V, which is nice- no separate regulator.
BTW, I don't know if you noticed this or not, but the Nyquist limit doesn't eliminate signals over Fsamp/2. Those components, if present, produce noise in the ADC data. And a simple RC filter does not have a sharp enough cutoff for this, there are some 2-stage active filters people often use. In general a codec chip will not need this hardware because they use oversampling- the ADC samples at a very high rate and they use a digital decimation filter to kick it down to the 8khz voice sampling rate.
I gotta note that making the filter costs about as much as just using the codec...