[PD] Jonathan Wilkes via Pd-list <pd-list at lists.iem.at>

[Simon Wise via Pd-list]

On 16/07/14 00:15, Dan Wilcox via Pd-list wrote:
> The onbopard audio might be better, but from what I could tell by the press
> release, it does't add a dedicated USB controller. In that case, it will
> probably still have the same issues with USB audio devices.
>
>> Anybody played with the new Raspberry Pi model?  It claims to haveimproved
> audio; I'm curious how that would effect a running instance of Pd on the Pi.

Haven't got mine delivered yet (it is on the way) but looking at the (minimal) 
schematics provided so far they have improved the power .. the miniUSB has gone 
up from 1.1 amps to 2 amps with a regulator added. Also the whole is said to 
draw significantly less power (why???) .. so other things have changed also. The 
USB/Ethernet hub has been changed to the 4-out version of the same chip, maybe 
this version is also better in other ways? I don't know if this hub is the 
problem for usb, or if the problem is the usb out of the main chip ... if the 
model A (without this hub) does better with usb audio cards than model B then 
the problem is here, but I have not got a model A to test with.

The board layout is completely new, so it might also be cleaner for audio? I 
will test noise and latency when it gets here.

I have just received 2 wolfson audio cards, which use the digital PCM link 
(rather than usb) and also expose another PCM link on a header plus a clock 
input (to the Pi header). They are quite flexible as far as clocking goes so 
several Pis could run these and share a single clock source (and pass digital 
audio between them), so I'll be testing that. It mounts onto the B-rev2 using 
the digital PCM on the 8 holes near the main 26 pin breakout. The B+ adds more 
GPIOs to a 40 pin breakout instead which include this stereo PCM link (and 
several others ... the clock, PWM and most of the digital interfaces can now be 
used simultaneously) but the digital audio is on different GPIOs so there will 
need to be some patching and some leads made up to use it on the B+. 
Unfortunately the wolfson card does not bring out the balanced audio pins from 
the chip (it has multiple DAC/ADCs) but instead it connects built in stereo 
mics, 2W amplified outputs and such.

The B rev2 schematics with the old power in and showing the low pass filter 
circuit on the PWM outputs providing the analogue audio:

http://www.raspberrypi.org/wp-content/uploads/2012/10/Raspberry-Pi-R2.0-Schematics-Issue2.2_027.pdf

or

http://www.raspberrypi.org/documentation/hardware/raspberrypi/Raspberry-Pi-Rev-2.1-Model-AB-Schematics.pdf

power is top of page 1, audio is lower right of page 2.

the new schematics with new power etc, with no mention of changes to the audio 
filter circuit (just the changes to the audio jack):

http://www.raspberrypi.org/documentation/hardware/raspberrypi/Raspberry-Pi-B-Plus-V1.2-Schematics.pdf

here is a photo with the new layout and new USB chip:

http://www.raspberrypi.org/wp-content/uploads/2014/07/rsz_b-.jpg


Simon