Modules
Making
Using
Details

Modules

The Dsp library uses modules as an abstraction type for generators and signal processors. A module is a Lua table with a __call metamethod so it can be called like a regular function.

Making

Modules are created using the Dsp:Mod() constructor. For example, the Pan module looks like this:

  function Dsp:Pan(init)
  
    local v1, v2
  
    return Dsp:Mod({
      description = "Pan",
      controls = {
        {
          id = "pan",
          description = "Pan",
          min = -1,
          max = 1,
          default = 0,
          fn_set = function(val) 
            v1 = math.min(1 + val, 1)
            v2 = math.min(1 - val, 1)
          end,
        },
      },
  
      fn_gen = function(i1, i2)
        i2 = i2 or i1
        return i1*v1, i2*v2
      end
  
    }, init)
  
  end

Using

To create an instance of the above module, call the constructor:

  pan = Dsp:Pan()

This wil generate a Pan module with default values. It is possible to initialize controls at construction time:

  pan = Dsp:Pan { pan = -0.5 }

Controls can be adjusted by using the set method.

  pan:set { "pan" = 1 }

To run the module, simply call the pan() object with the input samples as arguments:

  o1, o2 = pan(i1, i2)

Details

What's happening here:

  function Dsp:Pan(init)
  
    local v1, v2

Here the function is defined, with some local variables which will be available to the code below as upvalues

    return Dsp:Mod({
      description = "Pan",

Calling the constructor, which takes a table with the modules definition.

      controls = {
        {
          id = "pan",
          description = "Pan",
          min = -1,
          max = 1,
          default = 0,
          fn_set = function(val) 
            v1 = math.min(1 + val, 1)
            v2 = math.min(1 - val, 1)
          end,
        },
      },

These are the modules controls. The Pan module has only one which is called pan. This control ranges from -1 to 1, and has a default of 0. When changed, the fn_set() function is called.

      fn_gen = function(i1, i2)
        i2 = i2 or i1
        return i1*v1, i2*v2
      end

fn_gen is where the signal is generated; this function is called for each sample. The Pan module takes one or two inputs, i1 and i2, and generates two outputs, with the input signal panned left or right, depending on the v1 and v2 constants, which where calculated in the fn_set() function of the pan control

    }, init)

The constructor takes an optional init table with initial values for the controls.

  end

The end.