Flutter: How do I create an echo effect with the just_audio plugin?

I'm using the just_audio flutter plugin to modify a voice recording to playback as either high or low pitch. I now want to add an echo effect. For reference, you can do this in Audacity (see image below) - this is the effect I want to replicate using the just_audio plugin.

As a more general question - to what extent can the just_audio plugin be used to add a bunch of effects to a sound clip? Some examples other than echo would be playing with reverb, wet/dry gain, bass/treble, wahwah, etc.

just_audio provides an audio effects API which exposes the native audio effects available for a platform:

https://pub.dev/documentation/just_audio/latest/just_audio/AudioEffect-class.html

However, so far only a small number of Android audio effects are implemented, specifically the equalizer and loudness enhancer. It sounds like you want this one:

https://developer.android.com/reference/android/media/audiofx/EnvironmentalReverb

which isn't implemented in just_audio, so you would need to request it as a feature request on the project's GitHub page.