2 – Introducing the TASCAM
Limiting
Examine the 99:1 curve in the above graph. This setting reduces all sounds above the threshold to the same loudness. This is called limiting. Limiting is usually employed to allow a dynamic signal to be recorded at a maximum level with no risk that transient peaks will result in overload. In this application, the threshold setting (usually set relatively high) determines the extent to which the peaks will be limited.
Dynamic Expansion and Gating
Sometimes, it is desirable to increase the difference between the quietest signal and the noise in a recording by using a downward expander. A typical application would be eliminating room noises and breath sounds that can be heard between the phrases of a recorded vocal part.
The graph below shows the curveÉ<or a downward expander. Notice that above the threshold, the curve follows a 1 to 1 ratio (i.e., is unaffected by the gate). For each unit of input change below the threshold the output changes by two units. This is called a 1 to 2 expansion ratio.
As the input signal drops below the threshold, its output level drops at twice the rate it would using a 1 to 1 ratio. In effect, sounds below the expander threshold are “faded out” more quickly than they would be normally.
1 TO 1 RATIO
LOUDER
THRESHOLD
OUTPUT
LEVEL
1 TO 2 EXPANSION RATIO
LOUDER
INPUT LEVEL
When expanders use ratios higher than 1:10, sounds below the threshold are faded out very rapidly. This effect is called gating and can sound very abrupt. Adjusting the gate ratio can smooth out the abrupt change. The graph below shows the input/output curve for a typical gate.
1 TO 1 RATIO
LOUDER
THRESHOLD
OUTPUT |
|
LEVEL | 1 TO 99 EXPANSION RATIO |
|
LOUDER
INPUT LEVEL
Sounds that are louder than the threshold get “through the gate” unchanged. Sounds that are below the threshold are not heard. Gates can be used to great effect in processing drum tracks where sounds from the other instruments in the drum set leak through the mike of the instrument being recorded. Gates are also used frequently to “gate off” a reverb tail or the ringing from an insufficiently damped drum head.
Compression and Expansion
Combined
The
COMPRESSOR THRESHOLD |
| 4 TO 1 RATIO |
|
|
|
|
|
|
GATE THRESHOLD
OUTPUT |
|
LEVEL | 1 TO 99 EXPANSION RATIO |
|
LOUDER
INPUT LEVEL
Using this setting, levels above the compressor threshold will be compressed at a 4 to 1 ratio. Levels below the compressor threshold but above the gate threshold will not be changed. Levels below the gate threshold will be gated out completely.
TASCAM