SIGNAL PROCESSING:
Line level devices: adjust sound in various ways between source and amps.

FREQUENCY CONTOURING: Equalizers
Equalizer:  Sets of band-pass filters in series with potentiometers.
   Breaks entire spectrum into bands:
        each segment treated individually.

Tone controls:broad band adjustment.
   Treble boosts or attenuates highs freq.
   Bass boosts or attenuates lows freq.

"Loudness" switch and the Fletcher-Munsen curve.

Three-band Equalizers: often built into source modules of mixers.

Graphics Equalizer:  breaks bands into fairly distinct frequencies.
Good for selecting out very discrete problem frequencies.

Parametric Equalizer: bands that tend to overlap adjacent bands as well.
Adjustable by peak frequency, band width, and amplitude (gain).
   Gives smoother overall shape to the spectrum.
   Less ability to reject specific frequencies.

WARNING: DO NOT OVER EQ.
This can cause ringing at certain frquencies!

AMPLITUDE CONTOURING
Some devices alter the dynamics (loudness pattern) rather than the frequency 
of the sound.
Volumn Limiter:  used primarily for feeding recording devices.
   Does not affect sound at low levels, but limits sound above predetermined level.
   It gets just so loud and no more.
   Typically set somewhere below clipping point of system.
Compressor: acts on entire signal, both low gain and high.
   Effect increases with amplitude, affects loud sounds more than soft ones.
   Tends to compress the entire dynamic range rather than just establishing a 
   ceiling level.
Automatic Gain Control or AGC: keeps dynamics within a middle range.
   Boosts soft sounds and attenuates loud sounds.
   Brings all sounds to a given level, regardless of original level.
	* Severly alters original dynamics.
	* AGC analyzes sound as it occurs, but is always reacting:
	* Often slight delay between when it kicks in (the Attack Time) and kicks out 
        (the Release time). (You can often hear this happen in a recording.)
	* Ideal: a fast attack and a slow release.
AGC very common on small domestic recorders for recording level control:
   useful for voice-overs with background music.

SPECIAL EFFECTS:
Intentional distortion of the sound to make it sound "different" than original.
Reverb and Echo: in both, the original sound is fed back and heard again and again 
at lower and lower levels.

The difference:
   Reverb: the return is close enough to be heard as part of original sound.
   Echo: the return is heard as a separate sound.

In the analogue days, these effects require special devices.
Electronics has simplified this immensly.
Feedback: return is LOUDER than original, increases each time around until 
system driven into overload.