Perfecto mondo!
I was thinking we could use the serial eeproms -- one of the protocols
lets you extract consecutive bytes serially by providing clocking
pulses.  Then all you need is a PIC timer driving the eeprom to get the
sound.
David


Roman Black wrote:

> Hi, after all the discussion recently about doing
> sound on a PIC, 1bit systems etc, I came up with an
> idea to refine the process of 1bit encoding to be
> PIC friendly and it actually worked. It's fast enough
> to do 16bit to 1bit conversion real time at up to 156
> kbit/sec! It also gives good results with speech even
> with quite low bitrates. Great for making cheap
> talking remote controls and stuff for the visually
> impaired.
>
> Playback only requires one or two digital output pins
> and RC filter and very simple bitstream code.
>
> I played with a few systems, but the encoder that worked
> best was a closed-loop math model of the RC filter.
> Each new bit is decided by generating a possible
> hi and lo bit result, then models the analogue voltage
> that would occur on the RC filter, and picks the bit
> that gives the result closest to the original wave.
> Being closed loop simulation it follows the original
> wave quite well and gives good sound quality for
> low bitrates and very little record or playback
> hardware.
>
> I wrote some software that shows the waveform and
> the encoder waveform, with some adjustments to the
> encoding parameters. It models the RC filter and
> even tells you values of R and C to use.
>
> Then one button press to write the encoded bitstream
> to a data file or even a PIC .asm file with the
> sound data already formatted in "retlw" table
> format. You get a few seconds of speech on a 8kb
> PIC. Handy. :o)
>
> It's really a "PIC sound suite" that allows you to
> load your own sound waveforms in, view them, try
> different encoding formats and and see how the
> sound will turn out as it is plotted on screen.
> Then dump the bitstream data straight into your
> PIC. One thing I want to add is a RC filter attached
> to the PC parallel port, so I can hear the sound
> on identical hardware to the product, and know
> exactly how it will sound when the PIC plays it
> back later in the product.
>
> I wanted a system where I just had to push one
> button to add any sound or speech to any of my
> PIC projects, and it's pretty close to that. With
> the ability to record too, hmm, now I just need a
> few Mb of fast static ram...
> -Roman
>
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