15.1.6  Audio clip properties: channels bit_depth samplerate duration

The channels, bit_depth, samplerate and duration commands find properties of an audio clip.

• channels, bit_depth, samplerate and duration each take one argument:
  A, an audio clip.
• channels(A) returns the number of channels in A.
• bit_depth(A) returns the number of bits reserved for each sample value (8 or 16) in A.
• samplerate(A) returns the number of samples per second in A.
• duration(A) returns the duration of A in seconds.