Music Tech: Effects and processors

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Effects and Processors
Filtering
A standard volume control will change the volume of the whole audio signal. A
filter lets some of the audio signal through without changing it, but it will cut
or boost the signal level of a specific frequency range. An electrical circuit that
emphasizes or eliminates some frequencies from a signal. Filters are used in
electronic music to alter the harmonic content of a signal, which changes its
timbre. Examples of filters are: LPF (low pass filters) High pass (HPF), band
pass, notch and shelving filters. A filter just takes something away from the
signal but most of the filters used in music will have circuitry built in which
allows you to boost the signal as well.
Common controls on a filter
Different filters have different controls but these are the most important
controls:
Cut-Off frequency- determines which frequencies will be passed
unaffected and which ones will be cut
Centre frequency- determines the point at which a band-pass or notch
filter will have most effect
Gain control- determine how much cut or boost is applied to the
effected frequencies
Resonance or Q control- determines the bandwidth of frequencies
that are effected- a high value will affect a very narrow range and will
have the effect of audibly amplifying the frequency in a synth filter
circuit.
Slope- the slope of a filter determines how sharply the filter will act as
its cut-off frequency
LPF'S
Are instantly recognizable and very common. They reduce the level of all
frequencies above the cut-off frequencies but let the frequencies below the
value, pass througb unaffected. This can be heard on many dance tracks where
the drum part starts off muffed and gradually becomes clearer. LPF'S can be
heard on Madonna's ­ `The power of good bye' in the synth opening
HPF'S
A high pass filter does the opposite of a LPF. It lets frequencies above the cut
off frequency pass through unaffected and cuts those below. A common use of
HPF'S is as a rumble filter, where it is set at 80Hz to eliminated unwanted low
frequency sounds, many mixing desks included a switch on each channel for
this purpose.
Band-Pass filters
A band pass filter is the combination of LPF and HPF where any frequency
outside the scope of the LPF or HPF pass unaffected. When drawn on a graph it
looks like a bell curve. Band-pass filters allow the user to boost or cut the
effected frequencies and is commonly heard in wah-wah pedals.

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Notch Filters
Is a band pass filter with a very high Q value (A narrow bell curve) that is used
to cut out a particular frequency. It would often be used in location recording
to eliminate hum at a specific frequency.
Shelving Filters
Similar to LPF'S and HPF's as they work at either end of the frequency range
but a shelving filter allows you to cut or boost the signal beyond a certain
frequency.…read more

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Digital reverb-Artificial reverb became more controllable with new
technology. As technology advanced and became mass-produced,
compact digital units replaced the plates and springs used. Different
spaces could be emulated by adjusting parameters of the digital reverb
units:
Pre-Delay- time between the original sound and the 1st reflection. This can give
an impression of room size.
Early reflections- more spaced out, separated reelections of the original after
they have bounced off various surfaces.…read more

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Delay
Delay is an audio effect which records an input signal to an audio storage
medium, and then plays it back after a period of time.The delayed signal may
either be played back multiple times, or played back into the recording again,
to create the sound of a repeating, decaying echo.
Pitch shift
Pitch shifting is a sound recording technique in which the original pitch of a
sound is raised or lowered.…read more

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