Recording Glossary II
Another list of Recording gear and terminology
edited by Dan Frankowski
Liar's Club
this is taken from Dan's 4-Track FAQ
What is gain? What is volume? What is the difference?
Adapted from tstrohma@theodolite.ae.calpoly.edu (Trevor Strohman):
Gain occurs before the preamplifier stage, volume occurs afterward.
When to fiddle with each:
Adjust gain levels once, to find the optimal input levels for your
mixer/4-track: high enough for a good signal-to-noise ratio, low
enough for the desired level of distortion (usually none). Then
adjust volume controls to change the levels in the mix.
Lowering the gain reduces clipping and distortion. The gain also
helps even out levels: you don't have to have one volume slider
cranked while another is almost off to get a good mix. However, the
mix happens in the volume controls.
Cranking gain too high is much more likely to cause distortion than
cranking volume, and more noise occurs on low gain than on low volume.
What are decibels? When are they used instead of volts?
From a Webster's online dictionary:
deci-bel \'des-e-,bel, -bel\ n
[ISV deci- + bel]
(1928)
1a: a unit for expressing the ratio of two amounts of electric or acoustic
signal power equal to 10 times the common logarithm of this
ratio
1b: a unit for expressing the ratio of the magnitudes of two electric
voltages or currents or analogous acoustic quantities equal to
20 times the common logarithm of the voltage or current ratio
2: a unit for expressing the relative intensity of sounds on a scale
from zero for the average least perceptible sound to about 130 for
the average pain level
3: degree of loudness; also: extremely loud sound -- usu. used in
pl.
From the DAT-heads microphone FAQ:
"Noise is typically referred to in microphones in terms of equivalent
sound pressure level.. The measure used is typically dBA: decibels
above the hearing threshhold of 0.0002 microbar, A-weighted."
tstrohma@theodolite.ae.calpoly.edu (Trevor Strohman) writes:
A decibel is a logarithmic power level. Since mics output such tiny
signals in comparison to line levels, people use dB to talk about
levels. I'm not quite sure what all the levels are in relation to.
However, the formula for decibels is:
/ Vin \
dB = 10*log | ----- |
10 \ C /
Where Vin = the voltage you're measuring and C is the voltage you're
going to call 0 dB. I couldn't tell you in this case what C is, but
I'm assuming it's somewhere around 1 volt.
dB make the numbers more manageable. I can say "It's at -30 dB", or I
can say that "It's at one thousandth the voltage." Some mixers claim
a dynamic range of up to 90 dB or more! I'd rather say -90dB than one
billionth the voltage. I don't usually have reason to talk about
voltage of audio signals much.
Q1.1.1 What is an FX (effects) loop?
'FX' is the usual abbreviation for 'effects' in scripts and stage
directions.
An effect loop 'splits off' the signals on their way out of the
4-track (or mixer) and sends them to an external effects unit. The
output of that unit is then fed back into the output of the 4-track /
mixer. You can set, for each track, what level of signal is sent to
the effect unit, so you can have some tracks heavily treated and some
not treated at all.
For example, suppose you have 4 tracks of soaring music on tape,
including a trumpet. If you played the whole mix through a reverb,
it'd be like listening to it in a cathedral; unusably reverbed. Thus,
you want to add reverb to the trumpet.
The effect unit is set to produce a 'wet' signal because that's what
you want to feed back into the final signal from the 4-track or mixer.
Remember that this is being added to the original, untreated signal,
so there's no point in adding, for example, partially reverbed trumpet
to unreverbed trumpet. What you do is to choose the level of the
trumpet track which is sent to the reverb so that the right level of
reverbed trumpet is heard in the final mix.
What is noise reduction? What is Dolby? What is DBX?
See the rec.audio.pro FAQ for incredible detail about this.
There are two major families of noise reduction technology which
you're likely to find on 4-tracks: Dolby and DBX. These are each
discussed in a paragraph below.
There are (at least) three varieties of Dolby on cassette decks, but
they all work more or less the same way: whilst recording, they
enhance the high frequencies in the same area where hiss occurs.
During playback, they reduce those frequencies back to the same level
they were originally. This also reduces the hiss. You can play back
a Dolby-encoded tape without Dolby; the only effect you'll hear will
be a brighter, higher top end.
DBX processes the sound more severely than Dolby [and more
effectively?? --DSF]. If you record using DBX, you *must* play back
with it on. You may even find that a DBX-encoded tape from one
machine does not replay exactly on another.
What is EQ?
Thanks to Michael Parrott mparrott@kendaco.telebyte.com for a nearly complete rewrite for this question.
EQ (where each letter is pronounced: Ee-Kyoo) stands for
"equalization." As a noun, it means those controls on a recording,
mixing, or playback unit which allow for altering the tonal
characteristics of an audio signal by boosting (increasing) or cutting
(decreasing) the prominence of specific frequencies or frequency
ranges within the signal. As a verb, it indicates use of those
controls.
Michael Parrott mparrott@kendaco.telebyte.com writes:
"Note that EQ does not tend to make extreme changes in signal levels;
instead, it can be used to reduce or increase the prominence of
certain frequencies in the signal, which in turn reduces or increases
the audible prominence of certain portions of a track or mix. If you
get a chance to experiment, listen to what happens when you boost the
5 KHz range in an evenly-mixed guitar track; the guitar should become
more prominent in the mix without having significantly changed it's
signal level."
Different types of EQ:
- Parametric EQ (also "sweepable EQ")
A form of EQ which affects broad sections, or bands, of frequencies in an audio signal. May be found as either two controls (Low and High),
three controls (Low, Mid, and High), or four controls (Low, Mid, Mid
Freq, and High). They tend to affect frequencies in the following
ways:
Low: Boosts or cuts frequencies in the low (bass) half of the audible
frequency spectrum (20 Hz - 1 KHz). A "shelving" control, it tends to
make more extreme changes at very low frequencies (20 Hz) and less
extreme changes at higher frequencies (1 KHz).
Mid: Boosts or cuts frequencies in the mid range of the frequency
spectrum (100 Hz - 10 Khz). A "peaking" control, it tends to make more
extreme changes at the mid-range frequencies (around 1 KHz) and less
extreme changes at either end of the mid range (100 Hz and 10 KHz).
Mid Freq: Also seen as "Sweep", "Para EQ" and other variations. Alters
the center frequency or "peak" of the Mid EQ control. This allows the
Mid EQ control more flexibility in boosting or cutting frequencies
toward the lower-mid and upper-mid range of the spectrum.
High: Boosts or cuts frequencies in the high (treble) half of the
frequency spectrum (1 KHz - 20 KHz). A "shelving" control, it tends to
make more extreme changes at higher frequencies (20 KHz) and less
extreme changes at lower frequencies (1 KHz).
- Graphic EQ
A form of EQ which is generally designed to alter specific, very
narrow frequency bands in an audio signal. The number of controls may
vary from as few as three (effectively another form of parametric EQ)
to as many as 30 or more per channel, with the audible frequency
spectrum evenly divided among them. Controls are usually sliders, but
may also be seen as "plus-or-minus" buttons with an LED or flourescent
display indicating the amount of boost or cut for each frequency.
These controls are of the "peaking" type, centering on a specific
frequency with a small amount of overlap with adjacent controls.
The term "graphic" is used to describe this type of EQ due to the fact that the sliders (or other indicators), when set to most people's
listening preferences, tend to look like a sine wave or gentle curve.
Hence, a "graphic" representation of the EQ being applied to the
signal.
This type of EQ allows more precise control than parametric EQ over
the tonal characteristics of a signal and makes singling out specific
frequencies for boosting or cutting much simpler and more effective.
Different ways EQ is applied to the mix:
- per channel
Each input channel may be separately EQ-ed, as in a mixer.
- per bus
Each bus may be EQ-ed, where a "bus" is one of multiple destinations
for an output signal. Example buses: the master mix, feedback
monitors for the musicians, or the effects (FX) loop.
- global
The whole output sound may be EQ-ed. The tone controls on a hifi
amplifier are, therefore, global EQ.
What are balanced and unbalanced ins and outs?
reedijk@gene04.med.utoronto.ca writes:
An unbalanced signal pathway is identified by having two wires (RCA
plags, guitar jacks, some mic cables). These are high impedence and
are less desirable because as the cable gets longer, more noise is
introduced into the signal. A balanced siganl pathway has three wires
which is most common in Mics (SM 58 s for example). A few 4 tracks
have balanced inputs whcih means you can use better quality mics
without adaptors. AT RMX64s as far as I know are the only ones with
balanced outputs which you would use for hooking it up to high-end
gear (I' have yet to use them!)
What is the difference between a pre-amp and an amp?
reedijk@gene04.med.utoronto.ca writes:
Pre-amps ("pre-amplifiers") shape the character of the signal. This
is where the equalization and gain (sometimes distortion) are
controlled. An amp simply generates the raw power to push a speaker.
A bad pre-amp can distort the signal in many ways including clipping,
compression, poor frequency response (e.g. the "highs" disappear or
sound harsh etc.) or noise.
What is a MIDI sync device?
A "sync" (synchronization) device does two things:
- When you play a sequenced MIDI set of backing tracks to the sync
device, it will generate an audio signal that specifies the timing of
the MIDI. This signal (which is not at all musical, it sounds like
white noise or a modem) can be recorded.
- When the recording is played back to the sync device, it will
generate timing MIDI data to drive the sequencer.
In short, it allows you to synchronise a MIDI track (or many) being
played by a software or hardware MIDI sequencer to a 4-track recorder.
You require one track of the 4 for the sync signal. You don't need to
record the MIDI parts, since you can play them in sync with the tape
while you record the guitars, vox, etc (all the 'human' parts) on the
other three tracks of the 4-track. Finally, master the whole lot in
sync onto your DAT or whatever.
Remember, the *key* thing is that the MIDI parts don't ever need to go
onto any tape until you master. This means that you can adjust synth
balances, levels, etc right up until the final mix, and also means
that the synthesised parts will not suffer any degradation due to
being on tape; they're always 'first generation'.
Once again, the process is as follows:
- Record the MIDI sync track on your 4-track machine with a sync
device, having a MIDI device playing through the sync device
- Record the human tracks while using the sync device to play the
MIDI. The MIDI is not recorded; it is used by the humans performing.
- Play back human parts and MIDI parts (with sync device) onto a
master tape
Dan Frankowski works at Net Perceptions (http://www.netperceptions.com), improving algorithms for our collaborative filtering software,
GroupLens. work phone# (612) 903-1291, email: dfrankow@netperceptions.com.
Dan also plays in Liars Club, a "chamber ensemble of the 21st century." Hard-edged, original compositions.
