[linux-audio-dev] Re: Software controller for homemade edrums

[Olivier Guilyardi]

Ben Loftis wrote:

>>As you may see, scratching seems to work fine in here :-)
> 
> This is so incredibly cool!  Is this technique already in wide use somewhere 
> that I missed?  Because if not, it should be.  This means that all you need 
> for an electronic drum set is a multichannel sound card and some homemade 
> piezo-triggered pads!  And I think with some further experimentation with pad 
> materials and response files, you can probably come up with all kinds of 
> permutations on the sound.  I'd like to hear what this sounds like using some 
> traditional drum samples ( like a snare or an 808-style kick ).  I'm assuming 
> that the current samples lack "punch" only because they are from a piano 
> chord response file.

Guitar not piano ;-) As I said in my original mail, I tried with a snare drum, 
but it sounded like "very far". This may come from my snare drum sample though, 
because it has some silence at its end.

I do recognize that convolution allows to keep much of the caracteristics of the 
raw pad signal, and that is very cool. When playing (with hands) on these pads, 
I felt like it was a real drum instrument, because every little hit was 
hearable, and hitting the edges, sides or center caused subtle variations. In 
comparison to this, midi triggers look very limited, that is very true.

>>By the way, Ben, what do you think of my idea of coupling triggering with
>>convolution, as stated in my previous mail (above, third paragraph) ?
>>Here's a diagram to further describe this idea :
>>
>>pad signal ----> trigger detection ----> sample playback -----
>>    |                                                         |
>>    |                                                         |
>>    ------------------------------------->   convolution  <----
>>                                                 |
>>                                                 |
>>                                                 +--> output
>>
>>Would this be possible ?
> 
> 
> You essentially _have_ the drawing, above.  You just can't change the sample 
> on every hit.  I don't know what you expect to achieve.  Trust me, what 
> you've got now is much cooler than a triggered playback (although it does not 
> sound the same)

> It is possible that using a triggered sample or some sort of envelope follower 
> will be required to get the attack of a traditional drum sound.  I'm sure 
> there are lots of ways to improve this simple system beyond jack_convolve.  I 
> think you've stumbled across a really cool synthesis technique!

That's it, you understood why I had this idea : the "attack" of the sound. This 
chord sample I used is very short, and pretty "constant". What about longer 
samples, with a real attack and sustain ? Anyway, thinking about it, I'm not 
sure this is a good idea. I suppose the attack should be possible to obtain 
without triggering anything, or just some sort of envelope as you say.

I guess some important points are :
- tuning the convolution algorithm and its parameters for this specific task, if 
  possible
- using the right response files
- carefully choosing the pad material, and microphone position
- possibly applying some sustain/etc.. (ladspa) filters between the pad signal 
and the convolution engine
- a _lot_ of cpu ;-)

PS: Could anyone point me toward a document explaining the 
technical/mathematical details of convolution, especially about audio ?

Regards

--
   og