There are 1424 possible deltas given 89 steps and 16 codes. We can
quickly compute those and reuse them to save time.
Knowing the exact size of the waveform we can re-author the
decompression loop to take advantage of that. We can place the block
header decompression first in the outer while loop and then place an
inner loop with the 2 samples per block decompression unwrapped. The
first sample reads from the stream and the second uses the other 4 bits.
The number of samples in the ADPCM can be known once the data chunk is
extracted and the block size is known. From there the audio buffer can
be created and its channel data passed to the decompress method. A lot
of time is saved by writing to the channel data directly instead of
writing to one array, copying that to another array, and then finally
copying to the channel data. A surprising amount of time is saved by
using one getChannelData call instead of calling to store each sample.
