Transient Accenting

Gate Uses and Abuses

Gates were originally devised to reduce noise in the silent passages of music programme especially during the process of multi track recording on analogue tape.

They still get used to reduce noise but they have found many other uses and creative applications over the years.

Applications include:-

• Noise reduction
• Removing compressor breathing noise
• Reducing spill from adjacent sound sources
• Gating ambience reverb for effects
• Gating one instrument to sync it with another
• Ducking one source to make room for another in a mix
• Reduction of ringing on drums
• Increasing the definition and punch of drums

Very often the process of gating produces unwanted side effects especially if the gate is not set up well or does not operate sympathetically with a particular type of source material.

These can include:-

• Chatter (when the gate is indecisive and keeps opening and closing on sustained notes)
• Clicking (when the attack is set too fast or when it’s envelope shape is unsuitable and generates high order harmonics each time it opens)
• False triggering (when the gate opens on microphone spill as well as its intended source).
• Noise enhancement (when noise is removed totally, the transition from gate shut to gate open and back modulates the background noise so much that it draws the listeners attention to the noise when it is present)

Providing controls for threshold, attack, release, hold and ratio, plus good metering, will help operators set the gate up for differing signal sources and minimise most of the negative effects above. However, this may involve a degree of compromise between the desired gating effects and the unwanted side effects. The DN530 will fair better than most because design choices made during its development were based on listening tests carefully tailored to match real world applications.

Chatter

Chatter can normally be eliminated by increasing the hold time but this may allow the gate to stay open longer than is desirable. Adding hysteresis to the threshold control helps enormously and allows hold times to be reduced without signal chatter. The DN530 has 4dB of hysteresis built in which is enough to eliminate chatter on all normal instrument types.

Clicking

The key to silent gating is the shape of the gain transition curve that is used to fade up the signal level when the gate opens (attack) and fade it back down when the gate closes (release). Many gates use linear transitions which, applied to low frequency signals, generate high order harmonics that sound like extra clicks (in time with the music source). The ideal shape is log (like an audio fader) so that the initial transition from shut to mostly open is fast and the final adjustment to fully open is progressively slower and slower. The exact reverse applies to the gate closing; this needs to start slowly and then speed up to close the gate fully. With these shapes no harmonics are produced during an attack, only a fundamental frequency (quarter cycle) that can be controlled by the attack time.

The tonality of the gate opening transition can be adjusted using the attack control to be slightly higher in pitch than the LF content of the sound it is processing to accentuate the start of each note; or set to be the same, in which case the transition will not be heard at all. If the attack is made slower still the start of each note will be softened which may be useful as an effect. Release times are typically much slower so audio frequency clicks are rarely heard but the log shape is still the best because it makes the fade out much less noticeable. The attack and release characteristics in the DN530 are log and fully adjustable to ensure effective gating that can be tonally transparent or used to add (or reduce) punch and definition.

False Triggering

Often microphones pick up as much spill from other instruments as they do sound from the intended source. This will cause the gate to open at times when it should be shut. Traditionally hi pass and low pass filters have been employed on gates side chains in an attempt to limit the frequencies spectrum that will trigger the gate to open. This type of filter seldom works well in this application because they are not easily manufactured with steep enough transitions from pass band to stop band. Also set up is difficult because you typically need to adjust them together to form a band pass filter.

A much better solution is to use a band pass filter in the first place set up with a high enough Q to make it very selective. Most instruments (especially drums) have a resonant frequency and false gate triggering can be massively improved by tuning a single band pass filter as described to find this resonance. False triggering is eliminated because the frequency spectrum and resonance from the spill does not produce enough energy at the tuned frequency to open the gate; only the intended source will.

The DN530 side chain filters are a high Q band pass types as described above. Set up is made by a simple single control (per channel) and this is made even easier because you can listen to the filter output (without interrupting the source material) on a separate solo bus.

Noise Enhancement

We all have the ability to block out constant back ground noises and often using a gate to eliminating background noises altogether defeats this mechanism; drawing our attention to the noise when the gate opens. Typically adjusting the gate range down to 10 or 15dB produces much more natural sounding results.

Transient Accenting

Many instruments have a percussive start to notes that are played. These transients can be enhanced or reduced by careful adjustment of the attack time as described above. Additionally the DN530 has the ability to accentuate this transition even more through application of its Transient Accenting capabilities described below:-

Every time the gate opens an accent is applied. This is a controlled boost in the signal level that lasts approximately 30ms. The amount of boost applied is determined (in dB) by the accent control and speed at which it is applied is determined (in ms) by the attack control. The boost is gradually removed during the 30ms accent period returning the signal level to normal.

If the gate is being used creatively the effect of the gate opening transition can be accentuated, which is particularly useful on drums improving definition and punch.

The accent effect is totally independent of the range control so it is possible to reduce the range very low or even off (0dB) and still achieve noticeable enhancement of transients.

Some benefits from Transient Accenting are listed below:-

• Increased tonal shaping effectiveness – gates can be used to modify the leading edge of percussive sounds to add definition and punch. This effect can be massively increased by accenting if required.
• Reduction of gated breathing – the noise enhancement issues associated gating background noise can be reduced or totally eliminated while retaining the tonal shaping and punch that a gate can add to percussive sounds.
• Reduction of delay – when gates are used to re shape the transient start of a sound they remove a small amount of sound at the start. This effectively causes a slight delay. Digital gates can capture this sound by using look ahead techniques but they are not time machines; the way they work is to delay the signal until the gate has opened. This eliminates any losses from the transient but delays the signal even further. Using Transient Accenting with the gate range at minimum (0dB) ensures absolutely no sound is lost and no delay is introduced; however controlled accentuation of the transient is still possible.
• Reduction of resonant howl round – with high amplification levels it is possible for a drum to resonate in sympathy with the amplified version of its self similar to microphonic howl round. It is possible for this sound to be so loud that once open a gate will not shut again. If the sound levels are reduced and the drum transients are accentuated the possibility of howl round is substantially reduced. The Transient Accenting only lasts for 30ms so any risk of resonant build up is restricted to this time period only.

The Transient Accenting feature contained in the DN530 adds another tool for the sound engineer that can be used to enhance and compliment the application of gating to many types of sound source.