Issue
110, September 1999
Talking
Back: Adding Speech to Embedded Applications
by
Rodger Richey
Training
embedded apps to process speech may be as easy as
finding the right 8-bit micro. Don't let what Rodger
has to say about using an ADPCM algorithm and PWM
output to generate speech to go in one ear and out
the other.
The
ultimate form of feedback from a product is through
speech. A product that reacts to stimuli with a verbal
response is more likely to grab your attention than
one without the capability.
In
most cases, adding speech recording and playback requires
extra processor bandwidth or an additional device such
as a DSP or specialized audio processor. The cost, complexity,
or lack of additional bandwidth, however, can prevent
the speech features from being integrated into the product.
Now,
if the words "8-bit microcontroller" were
mentioned with respect to speech, some might chuckle
to themselves, others might break into a fit of uncontrollable
laughter, but certainly all would read on. Yes, it’s
true: A simplified Adaptive Differential Pulse Code
Modulation (ADPCM) algorithm can be implemented on a
low-cost 8-bit micro.
In
this article I explain the tradeoffs between bit rate
and quality that are important in determining if you
can use an 8-bit controller in the product. I also present
the details of the origin as well as features of the
ADPCM algorithm. Finally, I cover methods of integrating
the microcontroller into the application as a speech
encoder/decoder peripheral or as a complete speech-processing
subsystem.
