by Bryan Bergeron, Editor by Bryan Bergeron, Editor
DEVELOPING
Sound Off!
The ability to add complex sound to a project — be it
voice, music, or the chirping of angry birds — has never
been so easy or affordable. Given the popularity of
personal MP3 players, just about any song or sound
imaginable can be downloaded from the Web. Although
stand-alone versions of Seri aren’t yet available, large
vocabulary voice synthesis options are no longer tied to
expensive add-ons or desktop computers.
My current favorite for playing sequences of MP3
sounds is the Sparkfun MP3 player shield for the Arduino
($60), together with their 1.4W class D audio amp ($8),
shown in the accompanying figure. I included the
mechanical striker (or hammer) from a 50 year old piano
for a size comparison, as well as a reminder of how far
we’ve come in the production and reproduction of sound.
The mechanical striker is quite a piece of
craftsmanship — there are multiple layers of felt, chucks of
cork, leather, and carefully glued joints. It’s a one-of-a-kind,
and — together with the wires and other components in
an all-mechanical piano — creates a rich tone that can’t be
fully reproduced on consumer-grade electronics.
The MP3 shield with an accompanying amp, in
contrast, are stamped out in the thousands. Furthermore,
MP3 files downloaded from the Internet sound the same
on every shield. Some of the subtleties may be missing in
the audio playback, but most people don’t notice.
I like the shield as a sound-effects source because of
the ease with which MP3 files — stored on the onboard
Flash drive — can be accessed and played. For headphones,
it’s simply plug-and-play. However, if you need to drive an
amp that isn’t configured for the low impedance audio
output available from the headphone jack, then a pair of
the 1.4W audio amps are a necessity (one amp for mono
output). It’s possible to connect the MP3 player to a
different amp, but I’d rather not bother with the capacitors
and resistors needed to condition the output of the player.
I’ve also used the shield/amp combination with a
small surface transducer (also available from SparkFun)
that can transform a table top or plastic box into a
speaker. You’ll have to add a resistor to the amp to
increase the output of the amp so it drives the surface
transducer to full output.
When it comes to voice, it’s hard to beat the
price/performance of the Emic 2 text-to-speech module
from Grand Idea Studio/Parallax ($60). The Propeller-based board — which is only 1.23” x 1.5” — supports nine
voice styles in both English and Spanish. It uses the
DECtalk text-to-speech engine to provide dynamic control
for pitch, rate, and emphasis.
Last but not least, you should consider the Veho 360
speaker available from Parallax ($15). The golf ball sized
speaker provides 2.4W of output for up to eight hours. It
recharges in about four hours through a standard USB
cable. Trouble is, I’m going broke giving these things to
my nieces, nephews, and coworkers. Not only do they
provide a simple, compact output for the SparkFun MP3
player and the Emic 2, but they transform a diminutive
iPod into a boom box with amazing bass response. They
also double as Christmas tree ornaments — something to
consider in December. NV
PERSPECTIVES
6 November 2013
