Data Sheet

-133-
355. Digital Signal Processing
Connect points E and F with a 4-wire (4) in project #352. Hold the
magnet (7) near the reed switch (83) for a while and you will hear space
battle sounds in soft volume. This is because the 100W resistor (41)
limits the current through the speaker (93). Move the magnet (7) away
from the reed switch (83) and wait for a while. You will eventually hear
the space battle sounds start breaking up and fading out. Digital Signal
Processing consists of the process of performing ADC, processing the
digital bit stream in some way and then returning the signal to analog
through DAC. This could be done, for instance, on music signals (like
the ones stored in the 3-in-1 (11)) to improve the sound of the music.
This can help account for quantization errors.
356. Adaptive Pulse Code Modulation
Connect points G and H with a 4-wire (4) in project #352. Hold the
magnet (7) near the reed switch (83) for a while and you will hear music
in soft volume. This is because the 100W resistor (41) limits the current
through the speaker (93). Move the magnet (7) away from the reed
switch (83) and wait for a while. You will eventually hear the music start
breaking up and fading out. In order to reduce the quantization error
in the ADC process, Adaptive Pulse Code Modulations (ADPC) can be
used where the quantization level is not xed but varies. This way, for
the same number of levels, more levels can be placed where the analog
signal resides the majority of the time and fewer levels can be place
where the analog signal only briey resides This reduces the quantization
error because more quantization levels spaced closer together are used
where the analog signal resides the majority of the time.
357. Even Shorter Siren Fade Out
Replace the 470mF capacitor (74) with the 100mF capacitor (73) in
project #347. Press the press switch (61) for a while and you will hear
the siren in soft volume. This is because the 100W resistor (41) limits
the current through the speaker (93). Release the press switch (61)
and wait for a while. You will eventually hear the siren start breaking
up and fading out. Since there is a 100mF capacitor in this RC circuit,
the siren should fade out sooner than in project #347 where a 470mF
capacitor is used because the RC time constant in this circuit is about
1/5 the RC time constant of that in project #347.
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