[sdiy] Hardware convolution box?

[cheater00 cheater00]

There's also a way to dampen the reverb. Imagine a volume style pedal
that is normally up. Its level is recorded into a ring buffer that is
as long as the IR. At each output sample, the IR is multiplied
pointwise with the pedal's ring buffer before the usual convolution
operation happens. This lets you do something similar to damping a
spring reverb by touching the spring with your finger. On a synth
module it could be done with a pressure sensitive pad.

On Tue, Feb 14, 2017 at 2:09 AM, cheater00 cheater00
<cheater00 at gmail.com> wrote:
> There's plenty of choices for control over FIR based reverb:
> - envelope (especially decay and tails, but also attack and predelay)
> - companding (more or less noticeable body or tail)
> - shaping (same as companding)
> - filtering (brighter/darker with lpf and hpf)
> - EQ
> - pitch shifting (to change the pitch of the dominant modes of the room)
> - using multiple FIRs at once (which in the end is just one FIR which
> is longer so no increase in hardware demands really)
>
> Most importantly you have plenty exciting IRs already. And if you
> don't like the ones you tried, keep trying.
> Not everything has to have a million knobs. The piano has zero knobs
> and it works well. All this knob craze is just that, a craze, imo.
>
> Why not a laptop? There is a multitude of situations where dedicated
> hardware is preferable to "a laptop with vst on it". Do we really need
> to kick that dead horse? I'm sure there's a million posts that explain
> this already.
>
> On Tue, Feb 14, 2017 at 1:54 AM,  <mars at pingdynasty.com> wrote:
>> The main argument against straightforward convolution is the lack of
>> parameterisation, which is what I take Frédéric to mean by 'too generic
>> approach'.
>>
>> Yes, convolution can be used for great sounding reverbs, and a good IR
>> accurately captures the sound of any space. But it does so from one
>> particular place, in one room, in one state (empty, humid...), recorded with
>> one mic. You might get a 'wet/dry' knob but that's basically it.
>> And yes it can be used to accurately imitate any (linear, time invariant)
>> filter, but you don't get to control things like cutoff frequency, resonance
>> or anything else.
>> Same with cab emulations: one configuration, one mic position... It's like
>> finally getting your dream amp, only to find that all the knobs are stuck!
>>
>> There are of course tricks you can do to give the user more control, and
>> cross-fading across a table of IRs would be one of them. But you are then no
>> longer in the realm of straightforward convolution.
>>
>> There are plenty of software convolvers, but most people (from what I can
>> tell) tend not to use them for the simple reason that 'IR playback' just
>> doesn't give you enough control over the sound.
>> Actually why would you want a hardware convolution box, rather than a laptop
>> with unlimited IR storage?
>>
>> Convolution still has a place IMO as one part of a more complete offering.
>> The potential is massive, and I think there's an awful lot that can be done
>> once the performance hurdle has been overcome and the technology is more
>> accessible. It's like the early days of audio recordings; I say bring on the
>> (impulse response) wavetable synths!
>> But if all you want is a wax phonograph, maybe check this out:
>> http://www.logidy.com/
>>
>>
>> Martin
>>
>>
>> On 2017-02-13 21:13, cheater00 cheater00 wrote:
>>>
>>> Hi Frédéric,
>>>
>>> On Mon, Feb 13, 2017 at 9:49 PM, Frédéric (Opensource)
>>> <marzacdev at gmail.com> wrote:
>>>>
>>>> Hi cheater00,
>>>>
>>>> thank you for your didactic answer.
>>>>
>>>> I clearly understand the maths behind using an impulse response to model
>>>> a  transfer function. It's basically converting an approximation of an
>>>> unknown
>>>> function into a big huge FIR or a polynomial (z domain) of an extreme
>>>> high
>>>> order (as you prefer!).
>>>>
>>>> I think, for many musical applications, this is a (too?) generic approach
>>>> because
>>>> it does not benefit from the context (what you are actually modelling).
>>>>
>>>> You take the example of modelling "filters".
>>>> For audio DSP engines,  I often use IIR (or biquad) blocks in conjunction
>>>> with
>>>> various non-linear (well their polynomial approximation) elements.
>>>> How big has to be the equivalent FIR to get a satisfying similar impulse
>>>> response?
>>>> And how do you deal with alteration of the filter parameters (still an
>>>> example)?
>>>> Do you make a impulse response table (with interpolation ;-)) ?
>>>>
>>>> Same applies for complex delays ...
>>>
>>>
>>> I believe you're over-thinking this. A FIR filter will have its own
>>> sound, and that's it. It will be a different sound to analog, VA,
>>> component modelling, or FIR. Being able to change the cutoff in real
>>> time is not a challenge. I also think that the definition of
>>> convolution you're operating on is too low level. You're missing the
>>> forest for the trees. Convolution basically means "do stuff in the
>>> frequency domain" and "apply a volume and phase change based on
>>> frequency", that's it. You don't need to think about polynomials,
>>> FFTs, all that junk. That's too much conceptual load.
>>>
>>>>>> Furthermore the platform could obviously support any sort of synth, be
>>>>>> it physical modelling, string, component modelling, granular synthesis,
>>>>>> FM, PM, VA, sampler
>>>>
>>>>
>>>> I understand the platform as being the hardware, am I right?
>>>>
>>>> So what you ask is a generic box with MIDI ports, USB, audio in and out,
>>>> a
>>>> very
>>>> beefy CPU or/and DSP, fast memory and with a well documented and
>>>> accessible
>>>> SDK for anyone to develop for?
>>>>
>>>> Is that alright?
>>>
>>>
>>> Not really, no, we could just start by using dev boards, and see where
>>> that leads us, and then we can see if we can come up with a board that
>>> has some nice common features everyone would like to use. Some of the
>>> DSP dev boards have really good bang for the buck and unless someone
>>> proves to me otherwise I assume you'd be stupid to try and spin your
>>> own boards.
>>>
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>>
>>