Introduction to Music Production - Week 4
Greetings from sunny and dry Northern California, in the USA. This is Dennis Dillon with a lesson for week 4 of Introduction to Music Production at Coursera.org. I will be demonstrating the Gate audio effect found in Ableton Live 9. We will discuss the controls and visuals on the device.The gate is a dynamic processing effect, meaning that it impacts the amplitude of the signal being processed. Specifically, the gate "closes" to suppress the signal while its amplitude is below a threshold level, and the gate "opens" to pass the signal while its amplitude is above that threshold.
Basic Gate Function
Below is a snapshot of the Gate device in Ableton processing a sustained note played on electric bass. The orange horizontal line in the gate activity display represents the threshold. You may adjust the threshold by adjusting the threshold knob on the left or by selecting and dragging the threshold line in the display. The veritcal orange bar on the far right is displays the amount of gain reduction the gate is applying to the signal. The level of gain reduction may be adjusted by manipulating the Floor knob in the lower right corner of the Gate display. Turning the knob fully clockwise (0 dB) results in no gain reduction (as if the gate was turned off), and fully counter clockwise (-inf dB) results in maximum gain reduction.
The input signal is represented by the "off black" envelope in the background of the display. The output signal is represented by the light grey envelope with the white outline in the foreground. Here you can see that the output signal rises when the input signal rises above the threshold, and drops off sharply when the input drops below the threshold.
Time Adjustments
Adjusting the Attack changes the rate at which the gate "swings" from closed to open. Adjusting the Release changes the rate at which the gate "swings" from open to closed. Above the Attack and Release are set to their minimum values. Below, I have set the Attack and Release to longer times.
You can see that the output rise is not as sharp at the onset of the note, and that the output drop is more gradual. Audibly, the sound is missing the metallic attack typical of the electric bass, and has a more natural decay than the quick release.
The hold parameter sets the minimum time the gate will stay open. Below you see that the output does not immediately drop off when the signal dips below the threshold. This is because the gate remains open according to the hold time regardless of the input signal level. Once that time passes, the gate will then adjust based on the input signal.
What Is This Return?
The return setting optionally creates a second threshold level. Below you can see (with minimum hold time) that the gate opens as usual when the input signal exceeds the threshold, but the gate does not close until the input signal drops below the return level. (Return is always lower than the threshold.)
The return setting reflects the difference between the level to open the gate (threshold) and the level to close the gate (return). When the return setting is zero, there is no difference between the threshold and the return. Adjusting the threshold up and down, also moves the return level since it is relative to the threshold.
A Musical Application
Above you can see I am using the gate to suppress noise in the signal that is below about -35dbFS (the return level). This noise was apparent from my recording session and appeared to be emanating from my computer equipment. I was recording the bass signal too hot so the noise you see here is actually audible. While it would be preferable to go back and record everything again at the proper levels, here is a case where I was actually able to fix it in the mix (sort of).
Summary
The gate effect in Ableton Live 9 graphically displays the effect's impact on the input signal. The controls are organized with the threshold adjustments on the left, and the timing adjustments across the bottom. The strength of the gain reduction applied to the signal is also adjustable. The gate audio effect may be used to block out unwanted noise in recorded audio signals. The gate may also be used to alter certain characteristics of the sound by manipulating the amplitude envelope (e.g. softening the attack, or cutting off the decay).
Hopefully, you know a little more about the gate effect, how it functions and how it may be used in a musical context. Thank you for taking the time to read this week's lesson. Please let me know what you think of the content and feel free also to comment on the Ableton Live gate interface as compared to other digital audio workstations (DAWs).
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