[sdiy] Fast envelope generation

Martin Fay martin at martinfay.com
Wed Dec 19 08:41:30 CET 2012

Hi Don,

The deeper issue here is the hardware running the envelope code. On a  
32-bit CPU your position holds, but on 8-bit where higher precision is  
implemented with several lower precision operations this is not  
necessarily the case! Also lookup table efficiency is influenced by  
the memory architecture of the hardware, broad brush fast in relative  
terms on on 8-bit, slow on 32-bit.


Sent from my iPhone

On 19 Dec 2012, at 05:34, Donald Tillman <don at till.com> wrote:

> On Dec 18, 2012, at 5:06 PM, Tom Wiltshire wrote:
>> This is in serious danger of getting a bit religious, which is far  
>> from my intention, but here goes anyway.
> Aren't you welcoming of religions that are different from your own?   
> Don't worry, I'm not gonna whack you with my bible or anything.
> I'm very familiar with table lookups and interpolation.
> So how many multiplies per sample for this table look up?
>   1. interpolation part 1
>   2. interpolation part 2
>   3. scaling the exponential value to fit the step the envelope  
> needs to make
>   4. optionally recalculating the speed for dynamic parameter changes
> Is this correct?
> Wait a second; shouldn't the speed be a -exp(x) calculation?
> By comparison, the RC simulation is only one multiply per sample.
>  -- Don
> --
> Don Tillman
> Palo Alto, California
> don at till.com
> http://www.till.com
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