Yet another wave player, now NCO based and noise (almost) free

pik33 · 2012-07-19 01:30

This is at last what I wanted. No noise (of course there has to be some noise but compared to duty dac with or without dithering, this is much, much better)

And only one cog used.

This version uses NCO/PWM mode with 8 bit resolution, 7x oversampling, noise shaping and standard 80 MHz clocked Propeller

To do - compute constants in init procedure, to enable different sampling rates and overclocked Propeller without manually changing these constants in code and then place it in OBEX

pik33 · 2012-07-19 02:37

And sonething strange happens with this driver. I tried to add this to my player instead this duty dac used now, and then it don't work as expected, generating buzzing sound in one channel.

Then I discovered that these artifacts are caused by access to "bufnum" variable from another object - and only this variable - and only from another object (???), so I tried to change its place in my code.

I changed this:

VAR

  long cog
  long buf[512]
  long bufnum

to this

  long bufnum
  long cog
  long buf[512]

and it helped but I don't know exactly why. There has to be a bug somewhere.

kuroneko · 2012-07-19 02:56

bufcnt is a res which is used during sample location calculations without being initialised (NG: offset $0D06^A places it in the global stack area). With your variable swap it ends up at offset $4065 which is well clear of anything disturbing).

^A relative to buf[], in the archive posted in this thread

pik33 · 2012-07-19 03:12

Fixed, changed bufcnt from res1 to long 0 so it is initialized now. Thank you

Cluso99 · 2012-07-19 15:44

Nice work

Martin Hodge · 2012-07-20 07:02

What external circuitry does one need to test this?

pik33 · 2012-07-20 09:25

I use a Propeller demo board with sd card added on pins p0..p3 and standard audio out @ 10,11 (with corrected RC filters)

Any standard propeller audio environment will do. Base frequency is something about 308 kHz. (7x44.1)

cavelamb · 2012-07-20 09:59

Martin Hodge wrote: »

What external circuitry does one need to test this?

Powered speakers is all.

http://www.instructables.com/id/Building-a-custom-shield-for-the-Gangster-Gadget-P/step8/null/

pik33 · 2012-07-20 10:54

I added this driver to this player instead of duty dac one

http://forums.parallax.com/showthread.php?140767-A-new-topic-for-vga-(not-only)-sid-player (compile with bst, enable unused methods removing)

so you can try this driver there... The player uses modified Kye's driver so you can have your wav and dmp files in subdirectories on big (I use 8 GB) fat32 formatted SD and long (up to 32 chars) filenamed (the player reads LFNs)

Yet another wave player, now NCO based and noise (almost) free

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