expander ratio and range

[jithknot]

this has been driving me nuts for the past few days now
whet exactly is the ratio and range in an expander/gate??
from what me and my friends have deduced the range gives the ratio a space to work within between the range value and threshold (from eg if range is set to -20dB, the ratio only affects the signals dynamics between the threshold point (lets say -15dB) and -20dB below that, which means the ratio works between -15 and -35 dB).
so does that mean the signal below -35dB remains untouched or does it increase in volume without affecting dynamics.
another doubt i have is that since expander/gate works opposite to a compressor, does that mean the ratio works in the opposite manner as well?? i.e the ratio increases the signal by a fixed ratio rather than decrease it??

[Mark Bassett]

The range control on a expander/gate controls by how many dB the device will attenuate once the signal has dropped below the threshold. The range does not choose which signals are processed.

Both expanders and gates only affect signals below the threshold, these are either attenuated or muted.

If your threshold is at -15dB and range to -20dB, then when the signal drops below -15dB, the gate will turn the signal down by 20dB, to a level of -35dB, as you said (with an infinite ratio).

If the level is at -30dB, then it will drop to -50dB and so on.

Is the signal untouched if it is below -35dB? No. Any signal with a level less than -15 is attenuated by the range amount (with an infinite ratio).

"The ratio dictates how much the signal is attenuated by the expander. When using a ratio of 2:1, for instance, the expander reduces any signal below the threshold by two times. In this case, a signal that is 10dB below the threshold is reduced to 20dB below it; likewise, a signal that’s 2dB below the threshold is reduced to 4dB below it. Setting a ratio of 30:1 or greater turns the expander/gate effect to a gate. So, instead of lowering the levels of an effected signal, the signal is simply cut off". (Strong, J , Pro Tools for Dummies, 2nd Ed.)

Translation: If a signal is just above the threshold, nothing happens, if the signal just drops under the threshold (for a range setting of -20dB) it will immediately be 20dB down in level (with an infinite ratio).

However, you can use the ratio control to smooth out the transition between no attenuation, and -20dB attenuation. Put another way, a smaller ratio will spread the gain reduction over a larger input range.

A signal at -16dB will be attenuated by 20dB with an infinite ratio in the example, as will a signal at -20dB.

With a range of 2:1, a signal at -16dB (1dB under the threshold) will be attenuate by 2x1=2dB, a signal at -20dB (5dB under threshold) will be attenuated by 2x5=10dB, going down to a maximum of 20dB attenuation for signals at -25dB (2x 10dB=20dB=the range) and below.

Compressors and expanders/gates both reduce level, but their thresholds are reversed if you will. The ratio works the same way. A large ratio on a comp will yield more gain reduction, the same thing happens on a expander/gate. A 1:1 ratio does nothing on both a comp and expander/gate.

[heathen]

Also to add: Ratio on an expander is the same as compression, though works the opposite way, say a signal is being expanded by a ratio of 1:2 then it will expand a signal by double above the threshold. This way expanders can be used as basic noise reduction too, by setting the threshold just above the noise floor.

[Mark Bassett]

Yes, I was referring to downward expanders, not upward expanders.

[heathen]

Yes, I was referring to downward expanders, not upward expanders.

All cool, just thought I'd ummm expand on it. :)