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COMD 5070 Exam 1 Week 4 (Digital Systems) with Complete Solutions
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COMD 5070 Exam 1 Week 4 (Digital Systems) with Complete Solutions
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COMD 5070 Exam 1 Week 4 (DigitalSystems) with Complete Solutions
Aliasing - ANSWER-Process in which one sound is misrepresented as another.
If you record a signal at a sample rate that is too slow, there will be things happening in
the original signal that occurs between the samples that you take, resulting in
inaccuracy.
Higher frequency sounds happen quickly and will get lost in a recording with too low of a
sample rate.
Instead of disappearing altogether, these high frequency sounds are
misrepresented/recorded as lower frequency sounds.
One is the 'alias' of the other.
Aliasing Diagram - ANSWER-If you have a sine wave (red) going up and down at a
certain frequency, you would need to have a relatively high sample rate to catch all of
the peaks and troughs in this waveform.
However, the samples are only taken rather infrequently. Each blue dot is a sample.
If these blue dots were reconnected that have been only infrequently sampled, you
would get what appears to be a lower frequency sine wave (blue).
This wave is a misrepresentation/alias of the higher frequency red wave.
An analog recording can represent ... - ANSWER-An infinite number of points in time.
Or any possible amplitude value between the minimum and the maximum.
This cannot be fully represented by a table of numbers:
(In a table of numbers, each row represents the amplitude at a given moment in time.
(And you cannot have an infinite number of rows to reflect the infinite number of time
intervals that you could potentially look at in a signal that's truly continuous.)
It can only be represented by a graph.
Analog Signals - ANSWER-Analog signals are continuous in time and in amplitude.
, Continuous signals can be examined in any level of detail, and there would be no gaps
in the recording.
a line drawn on a page,
a microphone signal in a wire.
Analog to digital (ADC) conversion - ANSWER-If you record your speech through a
microphone, it is digitized.
It is turned into a series of numbers by the ADC system
Anti-Aliasing: Nyquist frequency - ANSWER-How to manage aliasing:
Set the low pass filter at the Nyquist frequency.
The filter will delete any frequencies above the Nyquist frequency so they are unable to
be misrepresented and contaminate the recording.
Most modern recording systems do the filtering for you automatically.
Anti-Aliasing: Using a Low Pass Filter - ANSWER-How to manage aliasing:
Use a low pass filter.
This will prevent higher frequencies from reaching the digitizing system so they won't
then contaminate the lower frequency recordings by being misrepresented.
Boosted Weak Signal - ANSWER-If only a few of the available value steps for amplitude
are used, it's really no better than having a system that cannot accommodate more than
just a few values.
As you boost it, the noise is also boosted, creating a bad signal-to-noise ratio.
Common Analog Devices - ANSWER-Show any possible values between minimum and
maximum ...
Clocks and watches with hands
(Hands rather than a changing numeric display),
Mercury thermometer
(Can display any temperature between the high and low),
Tape measures
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