# Load a single external synthdef

``

    load_synthdef  path (string)

Load a pre-compiled synth design from the specified file. This is useful if you wish to use your own SuperCollider synthesiser designs within Sonic Pi.

## Important notes

The binary file containing the synth design must have the extension `.scsyndef`.

You may not trigger external synthdefs unless you enable the following GUI preference:

`Studio -> Synths and FX -> Enable external synths and FX`

If you wish your synth to work with Sonic Pi’s automatic stereo sound infrastructure you need to ensure your synth outputs a stereo signal to an audio bus with an index specified by a synth arg named `out_bus`. Also, Sonic Pi makes no automatic attempt to free a synth once triggered, so to behave like the built-in synths, your synth needs to automatically free itself. For example, the following synth would work nicely:

    (
    SynthDef(\piTest,
             {|freq = 200, amp = 1, out_bus = 0 |
               Out.ar(out_bus,
                      SinOsc.ar([freq,freq],0,0.5)* Line.kr(1, 0, 5, amp, doneAction: 2))}
    ).writeDefFile("/Users/sam/Desktop/")
    )

Introduced in v4.0

## Example

# Example 1
``
    load_synthdef "~/Desktop/my_noises/whoosh.scsyndef"
| ``
    # Load whoosh synthdef design.