Drawing a waveform with an outline

anyone got suggestions on how to draw an outline for a waveform?  i've successfully used the AudioThumbnail class to render the basic waveform (for example, in black) and now i want to draw an outline in a contrasting colour (eg, white).





i got this done pretty easily with just calling drawChannels twice, with a slightly smaller size on the second call.

It feels inefficient, but perhaps it's ok?