[sdiy] Chris Synths polysynth

[Roman Sowa]

Or why not simply make sigma-delta modulator like in any audio DAC today?
Shouldn't take much of FPGA resources.

This morning I came up with an idea of PWM decoder giving solid output 
after single PWM cycle using 2 opamps and 4053, but it looked so obvious 
that I thought it had to be done before, so did some googling and found 
this, which is basicaly the same concept, but overly complex:
https://www.edn.com/pwm-dac-settles-in-one-period-of-the-pulse-train/

Roman

W dniu 2021-10-22 o 15:36, Mike Bryant via Synth-diy pisze:
> Good links.  They also led to this one where the writer suggests bit-reversing the counter to give a simple form of PDM replacing PWM.  Definitely an idea I'll bear in mind.
>
> https://www.edn.com/three-paths-to-a-free-dac/
>
>
>
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Steve via Synth-diy
> Sent: 22 October 2021 14:24
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Chris Synths polysynth
>
>
> I found these articles interesting, but have not tried in practise
>
> https://www.edn.com/cancel-pwm-dac-ripple-with-analog-subtraction/
>
> https://www.edn.com/fast-pwm-dac-has-no-ripple/
>
>
>
>
> Am 22.10.2021 um 12:15 schrieb Vladimir Pantelic via Synth-diy:
>> Arturia uses a dual PWM scheme in all of the their Keystep and
>> Beatstep products, basically following the circuit laid out here:
>>
>> http://www.openmusiclabs.com/learning/digital/pwm-dac/dual-pwm-circuit
>> s/index.html
>>
>>
>> it works nicely, BUT also introduces a >4ms slew on all CV outputs, no
>> biggie if driving an analog synth and it gets hidden in the attack,
>> but a real nuisance if it gets sampled by a digital module...
>>
>>
>> On 10/21/21 11:34 AM, Tom Wiltshire wrote:
>>> Here’s the correction:
>>>
>>> Imagine you have a DAC with 4-bit resolution. If we use one with a
>>> step-between-values of 1V, and then add the output of another with a
>>> step-between-values of 1/16th of a volt, we can make an 8-bit DAC.
>>> That’s basically what you do with the PWM. The process is helped by
>>> the very good linearity of digital-counter-based PWM as a method of
>>> producing a voltage.
>>>
>>> I’ve used a 3-bit PWM scaled to produce 1V per step and a 4-bit PWM
>>> scaled to produce 83mV per step to produce Pitch CVs. It worked very
>>> well and produced good CVs across the 8 octaves. The reduced bit
>>> depth of each PWM DAC means that the output frequency can be higher
>>> without the PWM clock frequency having to be super-high, and this
>>> improves the effect of filtering and the responsiveness of the CV to
>>> changes.
>>>
>>>> On 21 Oct 2021, at 09:54, cheater cheater via Synth-diy
>>>> <synth-diy at synth-diy.org> wrote:
>>>>
>>>> Correct me if I'm wrong, but I think summing two PWMs will just add
>>>> 1 bit of depth.
>>>
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