[sdiy] Stereo Audio CODEC ICs

[Seb Francis]

>A number of the converters whether they be discrete (separate ADC/DAC) or
>codecs is that they want to be clocked at a constant rate at certain
>frequencies. Some will not work varying the clock rate like you do with a
>BBD. Has to do with some of the digital filters and that they sort of use
>the clocking to do the conversion. They have internal integrators in these
>things that rely on a very accurate clock.
>
Yeah, I assumed as much.  Luckily this is what I want for my 
application.  I want to keep the sound quality the same while varying 
the delay time, so I will do this by changing the buffer size in 
software not the clock rate.

>Multi-bit converters seem to
>sound better to me than single bit. They are not as critical of clocking
>either.
>
>  
>
The Cirrus and Wolfson converters are multi-bit.  I'm not sure about the 
TI ones .. it's not clear from the datasheet.

>The layout of these on a PCB is extremely critical. Read all the app notes
>and data sheets on these things. It might be a problem using SMD adapters
>with these chips.
>
>  
>
Hopefully with careful layout and decoupling the SMD adapters won't give 
me problems, but I guess I will find out :)
Actually I plan to build this on stripboard (but I will break every 
stripboard track to the shortest required length so as to minimise stray 
capacitance between tracks).

>I've also found some the app notes and data sheets had the wrong values in
>their filters on the DACs. Can't remember if it was Cirrus or AKM I know it
>was one of the ones I used so those would be my choices. Might want to do
>the math and make sure they are right before you build something.
>  
>
What you do mean the wrong values in the filters?  You mean in the 
example applications?  I think these CODECs all have filters built in, 
so all that is required is external buffers.

>Also AKM makes converters. I looked at there disti and sales rep list on
>their web site. Didn't look good to buy just a few of them.
>
>  
>
Thanks, I'll check them out.   Hopefully I would be able to get some 
samples even if I'm not able to buy small quantities.

Cheers,
Seb