MUS 319

Study Guide:  Test Three

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Be able to provide a brief description of the following MIDI terms:

Aliasing/Foldover (see info below)
Click track
Default
Disc
Disk
Effects
Fader/Slider
Mute
Nyquist Frequency (see info below)
Pan
Parameter
SMPTE Time Code
Tweaking

Be able to describe how you would extend the range of any synthesizer beyond the confines of the given number of keys on the keyboard.  For example, if you needed all 88 keys of a traditional piano and your synthesizer only had 60 or so keys, what would you do to be able to record the entire range of the piano?

Be able to describe the easiest way to sequence record a transposed part found in an orchestra score.

Be able to describe how you would correct a wrong note that you recorded in a particular measure.

Be able to describe how you would make volume adjustments for:  an individual note, an entire track.

Be able to describe the shortcut for recording a repeated passage identical to the first.

Be able to describe the difference between Sound on Sound (a.k.a. overdub) and Overwrite modes.

Be able to list the number of individual channels in the standard MIDI network.

Above all, know what the acronym MIDI stands for!


Re Nyquist Frequency and Aliasing/Foldover ...

SAMPLE RATE / NYQUIST THEOREM--the sample rate must be at least twice the frequency of the highest sound frequency to accurately reproduce a waveform (sound).  E.g., if the highest frequency is the fundamental tone A440, the sample rate must be at least 880 Hz to capture the fundamental tone without distortion.  To capture the faster frequencies of overtones, the sampling rate must be increased (double the rate of the overtone frequencies).  

  • The Nyquist frequency is the frequency whose value is half that of the sampling rate.  Recording any frequencies higher than this pitch will cause unwanted distortion (aliasing/foldover).  In other words, the Nyquist frequency indicates the highest pitch which may be accurately sampled, given the sampling rate.

A good illustration of this principle can be found in weather.  To represent the annual fluctuation of the temperature outdoors, for example, it is necessary to record a thermometer reading once each January or so, and again exactly six months later, in July.  At this sampling rate of two "samples" per year, however, the daily fluctuation of temperature would not be detected.  To represent this additional fluctuation of temperature, it is necessary to record the thermometer level twice each day--once at midday and again exactly 12 hours later, in the middle of the night.  To represent both the annual and the daily temperature frequencies, then, requires a sampling rate of at least 730 temperature readings per year.

Example:  A waveform includes a fundamental frequency of 100 Hz and an overtone with a frequency of 400 Hz.  A sampling rate of 800 samples per second is more than adequate to represent the fundamental frequency, and is also sufficient to represent the frequency of the overtone.

Example:  A waveform includes a fundamental frequency of 150 Hz and an overtone with a frequency of 600 Hz.  A sampling rate of 800 samples per second is more than adequate to represent the fundamental frequency, but is not sufficient to represent the frequency of the overtone.  Instead, the pattern formed from the samples of the overtone is that of a sound with a frequency of 200 Hz.  This is called an alias, or foldover, frequency.  As is usually the case, this alias frequency is not a harmonic overtone of the given fundamental.

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