chip can be used to collect samples of audio levels at
seven frequencies (Figure 10).
By toggling the Reset line and then pulsing the Strobe
line a specific number of times, you can select the specific
frequency you would like to measure (Figure 11).
Now that we have a chip that’s capable of capturing
amplitude at multiple points in the spectrum, we need to
connect this chip to an equally capable microcontroller.
Steve chose the venerable PICAXE 20X2 chip.
By using its built-in Analog-to-Digital Converter (ADC),
we can sequentially take samples from each frequency of
Can You Hear Me Now?
When it comes to voice, frequencies below 400 Hz
are not typically associated with jaw movement. Most are
“plosives” associated with unvoiced sounds such as “t,”
“k,” and “p,” and when recorded, are actually amplified as
an artifact of the recording process (i.e., air expelled
during speech that impacts the microphone element).
Alternately, frequencies above 2. 5 kHz are typically
sibilant sounds such as “ssss”/“shh,” and the human
mouth normally produces these by bringing the teeth and
jaw together. This means the frequencies we can sample
from the MSGEQ7 chip for jaw motion are 400 Hz, 1
kHz, and 2. 5 kHz.
The ADC in the PICAXE allows us to sample the
amplitude on each of these frequencies with eight bits of
resolution (value between 0 and 254).
So, rather than the original one bit of resolution
offered by the Scary Terry circuit (i.e., ON and OFF) or the
two bits of resolution offered by the Jawduino circuit (i.e.,
OFF, LOW, MED, HIGH), this new design will allow us to
sample amplitude with
eight bits of resolution
(255 discrete positions)
across three distinct
frequency bands — quite
If we sample each of
these, we can get a clear
picture of when the jaw
needs to be open in order
to more closely model the
jaw position in relation to
an audio file.
Now that we know
what frequencies we need
to sample, we can begin
to build a system that can
sample the sound and
then move the servo.
The complete code to
do this is shown in the
block diagram in
42 September 2017
■ FIGURE 12.
DF Player Mini
■ FIGURE 11.
■ FIGURE 10. The even bands covered by the MSGEQ7