Pipes & Holes

The pipe operator (|>) and hole (@) define Akkado’s signal flow model.

The pipe operator |>

The pipe operator connects audio processing nodes, creating a signal flow graph.

// Signal flows left to right
saw(220) |> lp(@, 800) |> out(@)

This reads as: “Generate a sawtooth at 220 Hz, pipe it through a lowpass filter at 800 Hz, then pipe to the output.”

Why pipes?

Pipes make signal flow explicit and readable:

// Without pipes (harder to read)
out(lp(saw(220), 800), lp(saw(220), 800))

// With pipes (clearer)
saw(220) |> lp(@, 800) |> out(@)

The hole @

The hole (@) is a placeholder that gets filled with the signal from the left side of the pipe.

Single hole

When you use @ once, it receives the piped signal:

sine(440) |> out(@)
//           ^    ^
//           |    |
//           Both holes filled with sine(440)

Multiple holes

You can use @ multiple times in the same expression:

// Send signal to both filter and output
sine(440) |> lp(@, 1000) + @ |> out(@)
//                          ^
//                          Original unfiltered signal mixed back in

Hole with math

The hole can be used in calculations:

// Reduce volume by half
sine(440) |> @ * 0.5 |> out(@)

// Add DC offset
sine(440) |> @ + 0.5 |> out(@)

Chaining pipes

Build signal chains by connecting multiple pipes:

// Oscillator -> Filter -> Distortion -> Output
saw(110) |> lp(@, 800) |> saturate(@, 2) |> out(@)

Branching

The hole lets you create parallel paths:

// Dry/wet mix
saw(110) |> lp(@, 500) * 0.7 + @ * 0.3 |> out(@)
//          filtered (wet)    original (dry)

Examples

Basic synth voice

// Oscillator through filter with envelope
saw(220) * adsr(trigger(2), 0.01, 0.2) |> lp(@, 1000) |> out(@)

Effects chain

// Guitar-like processing
saw(110)
    |> saturate(@, 3)
    |> lp(@, 2000)
    |> delay(@, 0.3, 0.4)
    |> out(@)

Stereo processing

// Stereo spread
saw(220) |> out(lp(@, 500), lp(@, 2000))