[sdiy] Filter cut off DAC

[Tom Wiltshire]

Go half-way like Roman suggests with 12-bit and a bit of simple RC filtering. The steps from the DAC are small enough that they’re not perceptible anyway, and the filter smoothing can be set at something below your update rate so that you get a totally analog output. If you’re updating the DAC at 5KHz, it doesn’t have to be as low as 200Hz. Switching the filters in and out is a clever trick, but it’s a measure of how desperate they were back in the 80’s. It was common enough then (on top-end gear like the PPG Wave and the Oberheim Xpander, no less!), but it’s not what I’d do now.

Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================

> On 22 May 2018, at 13:55, paula at synth.net wrote:
> 
> Roman,
> 
> Indeed the PPG Wave uses 8bit DACs and has filters it can switch in an out.
> I was hoping to avoid the use of a filter (more parts = more cost), but it'll work out cheaper than a decent 16bit DAC.
> 
> Paula
> 
> 
> 
> On 2018-05-22 13:40, Roman Sowa wrote:
>> Do it 12 bit. All you need is resolution enough not to notice
>> quantization during parameter settings. Regardless if it's just cutoff
>> on that DAC, or combined with LFO and envelope, it's still the same
>> amount of filter frequency quantization, so if one cannot notice it on
>> turning cutoff knob, it will not be noticeable with other modulation
>> sources added either.
>> And if you need smooth - just add simple analog filter after the DAC.
>> Like 200Hz or so.
>> Roman
>> W dniu 2018-05-21 o 17:52, paula at synth.net pisze:
>>>> So what do you want to do that might push the design goal above 13 bit?
>>> Just thinking, if you add an EG to an LFO and a few other modulation routings I wonder if 12 bits is enough to keep things sounding "smooth".
>>> Paula
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