A gate can be thought of as a processor which silences (or significantly reduces) the audio passing through it if is below the set threshold. This can be useful for removing unwanted noise present in an audio signal, so the gate will close if the wanted signal is not present. For this to work correctly there must be a reasonable signal to noise ratio. Gates have other uses such as controlling the decay of drums, which we will look at in this tutorial.
An expander is similar, but is essentially a gate with a soft knee. An expander can be thought of as the opposite of a compressor, reducing the part of the signal which falls below the threshold by a set amount. The ratio of the Duende channel expander is fixed at 1:2, and the gate is at 1:20. Where as a gate will open and close almost exactly at the set threshold and reduce the signal to almost silence, an expander will reduce the gain according to the input level; the lower the level, the more gain reduction happens.
Load Tutorial 2 into your DAW; here you will see 5 audio tracks of a drum recording. Because we have the drums recorded separately, we can zoom in on certain aspects of the individual tracks to control their dynamics using the gate/expander section of the Duende Channel.
Solo the kick track and open the Duende Channel placed over it.
Play the track and you will hear that the kick track contains a significant amount of the snare bleeding onto it. This is a consequence of modern mic’ing techniques and is quite normal. However, it may not be desirable to have the snare present on the kick track, as it narrows the options available for treating the kick drum as this would influence the snare as well.
Now press the BYPASS ALL button to turn the gate on. Firstly you will hear that the snare drum has virtually disappeared. You can see that the green gain reduction meter is lighting up indicating the gate is significantly reducing the gain when the kick drum is not being hit.
Now look at the gate controls:
- The gate/expander button is set to GATE mode as the EXP button is not on.
- The threshold is the level at which the gate will open and close. The threshold has been set to +4db, meaning that the gate will remain closed if it receives any audio below this level, and open if the input level is above this.
- The hold time is the period for which the gate will remain open after it has received a signal over the threshold.
- The release is the ramp time taken for the gate to return to its closed status after the hold time has been completed.
- The range is the amount by which the gate will reduce the gain in its closed state, from 0-40db.
- The FAST ATT button selects how long it takes the gate to open once it has received a signal over the threshold. With the button down the gate/expander will open almost instantaneously, and up it will take a small amount of time to react.
Now try moving the threshold control up and note that if this is set too high, nothing will get through the gate and the audio is almost silenced. If the threshold is set too low then everything will get through the gate and it won't function.
Turn the range control to 0db and note that no gating takes place. This is because in its closed state the gate will reduce the gain by 0db.
If the hold is set too long it will let more than one beat through, and as you slowly increase this from 0-4 seconds you can hear the snare being let through.
The release time has a similar effect but is a ramp up to full rather than a held level.
If the FAST ATT button is switched out, the first part of the kick drum is missed as the gate is not opening fast enough to catch the initial attack. This is generally best left on FAST ATT for transient signals such as drums. The hi-hat track has had a similar gate treatment to make the notes slightly shorter therefore giving a tighter sound. As you can see and hear a gate is a very powerful tool for separating drum signals, but also gives you some control over the length of the individual hits and their attack and decay characteristics.
Now lets look at the expander mode and its use for reducing (not silencing) the low level aspects of a snare drum track, whilst leaving the high level parts untouched.
Solo the snare track and open the Duende Channel plug-in.
You can hear that the snare track contains a fair amount of hi-hat. It may desirable to reduce the level of the hi-hat as the snare can then be treated more independently, which in this case means compressing it and adding some reverb.
Now press the BYPASS ALL button to place the expander and compressor in circuit. Looking at the green gain reduction meter it can be seen that similar to the gate on the kick drum the expander is reducing the gain in between snare hits, but in a more subtle manner. If you now move the range control on the expander to 0db so it is no longer working, the hi-hats and ambiance present on the snare track is brought up in level, partly due to the use of the compressor, which is used to give the snare some extra punch. If the range control is now turned back to about 20db, a cleaner, tighter sound is heard.
Take everything out of solo and hear that the kick and snare have more definition within the drum mix, and the kit generally sounds tighter and cleaner. Further down the mixing process this may bode well as there is now more 'space' in the drum mix.
Often if you wish to use large amounts of compression on the signal, it can be a good idea to use a gate or expander before hand to compensate for the fact that the compressor brings up the low level information. Using a gate/expander and compressor in this series configuration gives the user a great degree of control over both the low level and high level information present with in an audio signal.
- Reducing unwanted noise, i.e. guitar amp hum
- Reducing ambient noise from bad recording environments
- Separation of drum recordings
- Control of attack and decay on drum recordings
- Reduction of headphone bleed on vocals, acoustic guitar and other instruments
- Increasing the dynamic range of a signal