Hi Jim and Jerry

The parametric equzlizer demo that comes with the VC33 DSK has several
features that will be worth looking into. Here are some things you
might be able to start with...

- The analog IO is stereo 48Khz at 20bit resolution.

- Board level drain is typically 100-150mA, but this is running full
tilt. Lower the clock rate and it will go down. Also to keep the noise
down, switching regulators were not used. With the bulk of the current
going to the 1.8V DSP core, you can do the math and figure that a custom
board using more efficient switchers could get the current down into the
50-70mA range without much trouble.

- Though not the best electrets (gotta be cheap) the board does come
with 2 electret microphones.

- The equalizer passband frequencies (10 left and 10 right), gains and
Q's are all adjustable.

- Generating white noise is about 4 cycles (see RAND.ASM). You would
want to feed this into a seperate filter and sum it into the final output.

- Floating point is a kind of poor mans logarithmic, and once you have
got your signal in the log domain it is easy to change the log base.

- This demo also includes an unbelievably simple (legal dpt says I must
say this) *patented* floating point ALU trick that shows how to reduce
the sensitivity of truncation noise (Log Differential Compression or
LDC). In general it shows how to get near CD quality sound with 0
(zero) mantissa bits. This could go a long way toward reducing any
additional oddities you might produce by changing the log base.

- Another interesting thing about LDC is that when it does produce
harmonic distortion, it tends to generate the 2nd harmonic, and none of
the higher orders. This too might be usefull as it can make things
sound more natural.

- A soft clipper is also included that can be turned on/off. Basically
if the signal reaches the clipping point the gain is immediately
adjusted down to avoid clipping. The gain then drifts slowly back up.

Hope this helps,
Keith Larson

Note: For simple analog IO protection the op-amp output goes through 470
ohm resistors. Either use an inline amp or a pair of headphones with
fairly hi-z. Most headphones work pretty good.

+------------------------------------------+
|Keith Larson |
|Member Group Technical Staff |
|Texas Instruments Incorporated |
| |
| 281-274-3288 |
| [email protected] |
|------------------------------------------+
| TMS320C3x/C4x/VC33 Applications |
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