Elenco Snap Circuits® Deluxe Sound & Light Combo - Manual (Page 22)

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Sound in Our World
On your U26 keyboard, the blue keys
approximate the 5th overtone notes, and the
green keys approximate the 6th overtone
notes; actual frequency may vary from the
musical scale. The tone of the green keys can
be adjusted with the tune knob, allowing them
to be in tune with the blue keys, or out of tune
with them. The tone of the green keys may
also be adjusted using external resistors and
capacitors, which can change the frequency
range dramatically (and even beyond the
hearing range of your ears), and can create an
optical theremin. Your keyboard can play one
blue note and one green note at the same
time; if you press two keys of the same color
at the same time, only the higher note will be
played. Projects 186-189 and 210-212
demonstrate the capabilities of the U26
keyboard.
On most instruments, when you play a note
the sound produced is initially loud and then
decreases with time. On your U26 keyboard,
a note ends when you release the key, unless
you connected external resistors to produce a
continuous tone. More complex electronic
instruments can simulate more notes at the
same time, have more advanced techniques
for producing overtones, and continue to play
the note with decreasing loudness after the
key has been released.
The musical world’s equivalent to frequency
is pitch. The higher the frequency, the higher
the pitch of the sound. Frequencies above
2,000 Hz can be considered to provide treble
tone. Frequencies about 300 Hz and below
provide bass tone.
Up to now, the musical measures of pitch and
loudness have been discussed. But many
musical sounds have the same pitch and
loudness and yet sound very different. For
example, the sound of a guitar compared to
that of a piano for the same musical note. The
difference is a quality known as timbre. Timbre
describes how a sound is perceived, its
roughness. Scientifically it is due to differences
in the levels of the various overtones, and so
cannot be expressed using a single number.
Now consider the following two tones, which
differ slightly in frequency:
If they are played at the same time then their
sound waves would be added together to
produce:
Notice that the combined wave has a regular
pattern of where the two tones add together
and where they cancel each other out. This is
the effect that produces the beat you hear in
music. Two tones (that are close in frequency
and have similar amplitude for their
fundamental and for each of their overtones)
will beat at the rate of their frequency
difference. Rhythm is the pattern of regular
beat that a song has.
Now observe this tone:
The frequency is slowly increasing and
decreasing in a regular pattern. This is an
example of vibrato. If the frequency is
changing slowly then it will sound like a varying
pitch; a fast vibrato (several times a second)
produces an interesting sound effect. The
alarm IC (U2, included in Snap Circuits ®
models SC-100, 300, 500, or 750) produces
sounds using the vibrato effect.
Tempo is a musical term, which simply
describes how quickly a song is played.
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