Convert Sample type bit depth control is broken

Steps to reproduce:

• Open an audio file
• Choose Edit -> Convert Sample Type from menu bar
• Set the 'Bit depth' control to 4 bits
• Hit OK

Expected result

• Audio samples are quantized to 16 levels

Actual result

• Audio samples are quantized to 256 levels (8-bit)

You'll notice that the Y axis of the waveform changes to 'samp' with values up to 256. If you correspond the samples of the quantized waveform to the axis gradations, you'll see they correspond to these 256 values, not 16 values.