Updating audio parameters

[ben-denham]

I'm really enjoying using this library along with leipzig for web-based music generation, they're really great.

I was wondering if there was any recommended pattern for updating an AudioParam of a node that is part of a synthesizer? For example, I would like to be able to bind the gain parameter of a gain node to some dynamic value based on a slider from an <input type="range"> element:

(defn ping [freq]
  (connect->
    (square freq)
    (percussive 0.01 0.4)
    (gain dynamic-value-here?)))

I've been trying various approaches involving calling AudioParam.setValueAtTime() from an event listener and using an AudioBufferSourceNode to provide a changing value to other nodes, but nothing I try seems to work correctly.

If work is required to the library to be able to support something like this, I'd be happy to help out if I can.

[ctford]

Hi @ben-denham,

Sorry for the delayed response. I've been away from Github over the new year. Thanks for using CLJS Bach.

When you say you want the value to be dynamic, do you mean that you'd like to vary the slider in the middle of playing a note? As I read your code above, it seems to me that the slider value would be closed over at the time that ping is called and would remain the same for the life of the synthesiser instance. That would mean that you couldn't do cool effects like varying the volume smoothly in the middle of a piece.

I've never tried to solve your exact problem, but I suggest that a way to approach it is to look at how plug works -

cljs-bach/src/cljs_bach/synthesis.cljs

Line 49 in 2215b8d

(defn plug [param input context at duration]

.

plug is the function that CLJS Bach uses to attach an input to a synth node. gain, for example, uses plug to attach the gain level to the node.

The interesting part of this from your point of view is that plug works with both numbers and nodes, as you can see from the link above. If what you pass to gain were e.g. another node, then it could have a dynamic output respected by the gain node.

So I suggest creating an ordinary gain node with .createGain outside the scope of the synthesiser and then passing that to the gain in your synth. If you then call mutating methods on that original gain, that should be reflected immediately by any running synthesiser instances.

Does that make sense? A warning, I've only thought this through, not tried it myself!

[ben-denham]

Thanks very much for your response @ctford, and apologies for the super-delayed reply, I haven't had much time to work on my musical coding lately.

I discovered that support for ConstantSourceNode (https://developer.mozilla.org/en-US/docs/Web/API/ConstantSourceNode) was recently added to the web audio API, and it seems to provide the exact functionality I was looking for.

I've created a pull-request (#5) to add some useful functions for working with ConstantSourceNode if you think it is a useful addition to the library.

Cheers!