Layout of the visdata[2][2][576] argument to the render function.

Clearly the 576-length array is the actual samples.  The middle array
represents the audio channel, so left or right.  The left-most array represents
the two types, waveform and spectrum data.

visdata[0][0] = Spectrum, left.
visdata[0][1] = Spectrum, right.

visdata[1][0] = Waveform, left.
visdata[1][1] = Waveform, right.
