Guide to 768k PCM

Technical questions regarding the xTIMEcomposer, xSOFTip Explorer and Programming with XMOS.
en2senpai
Junior Member
Posts: 4
Joined: Mon Jul 19, 2021 7:32 am

Guide to 768k PCM

Post by en2senpai »

Hello,

is there any official or known to work manual how to achieve 768k PCM USB audio ?

I found couple of unanswered or old topics like:

https://www.xcore.com/viewtopic.php?f=2 ... 68k#p38900
https://www.xcore.com/viewtopic.php?f=2 ... 68k#p36830
https://www.xcore.com/viewtopic.php?f=37&t=8193

Based on informations i found, there are only few things to change in reference project:

#define MCLK_441 (1024*44100) /* 44.1, 88.2 etc */
#define MCLK_48 (1024*48000) /* 48, 96 etc */
#define MAX_FREQ (768000)

And here is my main question:

Do I need external ~45 MHz and ~49 MHz oscillators ?
Can this be achieved on ~22 MHz and ~24 MHz default ones ?

On standard clocks, my audio is being played, but its quite noisy.

Any help would be very nice !

Best


mmar
Experienced Member
Posts: 76
Joined: Fri Jul 05, 2013 5:55 pm

Post by mmar »

Do I need external ~45 MHz and ~49 MHz oscillators ? YES
Can this be achieved on ~22 MHz and ~24 MHz default ones ? NO

Need little more changes as three lines...
en2senpai
Junior Member
Posts: 4
Joined: Mon Jul 19, 2021 7:32 am

Post by en2senpai »

Hi !,

thanks for your response. Could you please clarify, what other changes are need to be done ?

Best
User avatar
akp
XCore Expert
Posts: 548
Joined: Thu Nov 26, 2015 11:47 pm

Post by akp »

I think technically it could be done with the 22/24 MHz default oscillators but those would support 16 bit I2S only, not 32 bit (768000 Hz * 2 * 16 = 24.576 MHz). So you'd have to do a rewrite of the I2S code to support that.