[sdiy] Digital delay memory

Jay Schwichtenberg jays at aracnet.com
Wed Apr 27 20:29:03 CEST 2016


I've been thinking about doing some DSP stuff and delay line stuff with the
newer MicroChip PIC32MZ series of processors. They're not really cheap but
have up to 512K bytes of internal RAM and an I2S interface. When start to
think about putting something together with SPI RAM with your time, board
space and PCB development then to me the extra cost becomes trivial.

https://www.olimex.com/Products/PIC/Development/PIC32-HMZ144/resources/PIC32
-HMZ144_UM.pdf
http://www.digikey.com/product-detail/en/olimex-ltd/PIC32-HMZ144/1188-1160-N
D/5247127

We see a lot of little ARM boards come out like the Teensy/Arduino for
example. I'd like to see something like that with a higher end ARM chip on a
bigger board with USB and bootloader, external fast ram and more pins broken
out. That to me would be a good basic platform for doing a whole lot of
stuff. Main problem for hobbyists like us is most ARM chips that have an
external memory interface are in BGA (Ball Grid Array) packages. These would
require some form or reflow soldering. Some people have used toaster ovens
and hot plates to do that but it sounds pretty tricky for the average
person. Also the boards would probably have to be more than 2 layers with
buried and blind vias.

Good luck.
Jay S.

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of
Richie Burnett
Sent: Wednesday, April 27, 2016 9:23 AM
To: synth-diy DIY
Subject: [sdiy] Digital delay memory

Tom and Eric, have you looked at the 23LC1024 SPI SRAM chip to supplement 
on-board delay memory?  (1MBit external static-RAM in 8-pin SOIC/TSSOP 
package for a couple of bucks.  A couple of seconds delay at 32kHz/16bit.)

I found that the hit for the SPI exchange wasn't too bad if you're doing 
your audio processing in blocks.  You can arrange DMA to "page in" or "page 
out" a block of external memory into the DMA RAM space in the background 
whilst doing other processing, so that it is there just ahead of when you 
want to use it.

It's good for things like digital delay memory.  Less so for reverb where 
you need lots of read/writes and the memory bandwidth over SPI becomes 
limiting.

Also had good success with old computer DRAM simms for *loooooooong* audio 
delay.  (Made a profanity delay for broadcast applications.)  All the 
RAS/CAS/refresh stuff isn't really that hard to implement for the old 
page-mode or EDO chips, and you could pick them up cheap on ebay.  It 
requires more I/O lines than SPI, but not as much as parallel SRAM.  Haven't

tried interfacing to modern Synchronous DRAM though.  It looks a lot more 
complicated!?

-Richie, 

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