The previous sine wave cast signed integers into the PCM range, causing
jumps at zero transitions. This shifts everything up by the respective
maximum signed integer, so that the signed idle zero becomes the
unsigned PCM signal's idle half-point and can continuously cover the
whole unsigned range.
The "Hello World" sample is really hard to hear on the noisy DAC / speaker
setup on my same54-xpro.
Replace it with a clearer sample from Wikimedia Commons and fix the ffmpeg
command line.
The set default is good enough for single-channel board, but whenever
DAC_DDS_CHAN is not zero (or even when a board has more), this may need
changing.
This will play a raw audio (8kHz, 8 Bit) snipped from the 1961 synthesized speech demo.
(Can be disabled since the file is rather large with 17k)
It will also play sine, square and sawtooth waves with frequencies that can be set on
the command line.
I tested this with the on-board speaker (connected to P0.26) of the mcb2388 as well
as with hooking up a headphone to the ANALOG (PA02) header of the same54-xpro.
