Mark Rages wrote:

> Initial results are here:
> http://vivara.net/modulator_test/
> 
> "in.wav": my input file
> "out_sd1.wav" : Sigma-delta first-order
> "out_sd2.wav" : Sigma-delta second-order
> "out_rb1.wav" : Roman Black 1-pin
> "out_rb2.wav" : Roman Black 1.5-pin
> 
> A note about all of these files:  No attempt to simulate the output
> filter has been done, except the output resampling filter, which is a
> windowed sinc filter at about 3200 Hz.  This puts the 1.5-pin result
> at a disadvantage, since it's encoded for a decoding that isn't taking
> place.

I'm not sure I understood what you did here. The way I think this works is:

- You have an audio signal, sampled at 8000 Hz (125 us steps) with a high
resolution.
- Since you said that the delta sigma sample rate is 19200 Hz (52.1 us),
you probably treated the input either as steps, or interpolated. 
- For every delta sigma sample step, you applied one of the four
algorithms. (Which Tc did you choose for Roman's algorithms?)
- The output here is a bitstream (or in the case of Roman's 1.5 bit
algorithm a double-bit stream) with a sample rate of 19200 Hz. 

(BTW, three of the bitstreams you created are 19.2 kb/s, while the 1.5 bit
algorithm at this point is a bitstream of 38.4 kb/s. Not quite a fair
comparison -- no wonder you were impressed :)

This bitstream would be what would have to go into the embedded storage.
Now that needs to be converted back into a wave file for listening,
simulating what would happen in the embedded system. So:

- Transform the bitstream into a pulse signal with two (or three, for the
1.5 bit algorithm) levels at a sample rate of 19200 Hz.
- Run this pulse signal through a single pole lowpass according to the
chosen Tc for Roman's algorithms, and through a lowpass of your choice for
the delta sigma algorithms.

Is this what you did? 

What seems to be odd is that your 2nd order DS signal is the worst -- when
everybody seems to say that increasing the order improves things. You're
sure there's nothing that can/should be tuned? Integration rates maybe?

Thanks,
Gerhard

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