[sdiy] Digital Audio CODEC config help

[Richie Burnett]

Worked a treat! Thanks.

I was able to generate stereo audio at 46.875kHz, 93.75kHz and 187.5kHz, 
using AK4556 with 24MHz MCLK and only changing the SAI divider ratios for 
BCLK and LRCLK in software to choose the sample rate.  (The strange sample 
rates are because the maximum frequency the Kinetis can generate as MCLK is 
24MHz, due to CPU clock speed limitation.)

The SAI can be configured to be clocked from an external 24.576MHz MCLK 
signal and still act as I2S master so I'm ultimately going to go with that 
so it can hit the standard sample rates of 48/96/192 kHz.  The 24.576MHz 
MCLK signal from a decent oscillator module will also likely have less 
jitter than the 24MHz signal divided down from the ARM CPU's PLL output!

Haven't connected the ADC part to the micro yet, but looping the CODEC's 
DOUT signal back to it's DIN pin resulted in stereo audio being passed 
through the ADC to the DAC outputs.  So, all looks good.

-Richie,



-----Original Message----- 
From: Mike Bryant
Sent: Wednesday, August 17, 2022 4:19 PM
To: Richie Burnett ; synth-diy mailing list
Subject: RE: [sdiy] Digital Audio CODEC config help

> Am I right in thinking that my choice of Mode 8 (or your Mode 4 choice) 
> would let me run the CODEC at Fs=48kHz, 96kHz, or 192kHz, with a fixed 
> MCLK frequency,

In theory yes.  MCLK should be 24.576MHz and you just alter FS to suit.

However, I recall some AKM chips had issues with running at 512x clock for 
48kHz sampling, though I can't remember if it is this particular chip as I 
always only use 96kHz.


> I also dabble with ultrasonic stuff in my day job so being able to go up 
> to 192kHz would be nice

You might get the DAC to do this, sort of, using de-emphasis mode 1, but the 
ADC will always kill anything over 20kHz I believe.  You'll need a different 
chip for that, probably an Analog Devices one.




-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Richie 
Burnett
Sent: 17 August 2022 11:52
To: synth-diy mailing list
Subject: Re: [sdiy] Digital Audio CODEC config help

> Yes Mode 8 should be fine for you.  I always use I2S and Mode 4 with
> the STM version of the SAI interface, but LJ should be ok

Thanks Mike.  I was kind of heading in that direction but wanted to be sure.

Am I right in thinking that my choice of Mode 8 (or your Mode 4 choice) 
would let me run the CODEC at Fs=48kHz, 96kHz, or 192kHz, with a fixed MCLK 
frequency, just by re-programming the SAI on the micro?  (This would be 
useful because for some projects I might want 48kHz, others 96kHz, and I 
also dabble with ultrasonic stuff in my day job so being able to go up to 
192kHz would be nice.)

I'm trying to get my head around the difference between Mode 8 and Mode 9.
It looks like Mode 9 is for a fixed sample rate ("Normal Speed") but lets 
you use different oversampling ratios for the MCLK?  ...and conversely Mode
8 allows you to support different sample rates ("Quad Speed", "Double Speed"
& "Normal Speed") but using a fixed MCLK frequency?  Am I understanding this 
correctly?

I know that a CODEC in slave mode can determine some information about the 
ratios of the different clocks by counting the number of cycles of the Bit 
Clock and Master Clock in one cycle of the Word Clock.  The configuration 
pins presumably provide the missing information it needs to operate as the 
user desires.

-Richie,

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