Data Sheet

-98-
200. Equalizer
Build the circuit shown on the left and turn on the switch (62). Press
the press switch (61) and you will see the bi-directional LED (71) and
colorful LED (72) light and hear the alarm (78) sound. Release the
press switch (61) and the bi-directional LED (71) and colorful LED (72)
will stay bright for a while then turn dim and the alarm (78) will sound
for a little while then turn off.
The sound from the alarm (78) is just a tone, but if it played music
with a range of frequencies, then you wouldn’t want to amplify all the
frequencies the same like in this circuit. Equalizers are lters that
modify the audio amplitude of specic frequencies to prevent distortion
and optimize the sound of music to our ears.
201. Decibels
Replace the 470mF capacitor (74) in project #200 with the 100mF
capacitor (73) and turn on the switch (62). Press the press switch (61)
and you will see the bi-directional LED (71) and colorful LED (72) light
and hear the alarm (78) sound. Release the press switch (61) and the
bi-directional LED (71) and colorful LED (72) will stay bright briey then
turn dim and the alarm (78) will sound briey then turn off.
Decibels (abbreviated as dB) are used, among other things, to measure
audio volume level. It is often used to dene large differences between
audio levels. For instance, if the audio power of a signal initially is P1
and then the audio power level of the signal is increases to P2, then
the audio level would be said to have increased by 10*log(P2/P1) dB,
where log represents the log base 10 function.
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