Shelving Filters & Compression

• Q (quality factor) dictates the bandwidth in an HPF notch filter; a larger Q narrows the bandwidth, and vice versa.

Shelving Filters

• Low shelving filters (LF shelf) can increase or decrease frequencies, whereas notch filters only attenuate.
• LF shelf attenuates from a specified frequency down to 20 Hz.
• High shelving filters attenuate from a set frequency up to 20 kHz.
• LF peak filter resembles a hill shape.
• An RTA can be used with pink noise to identify frequencies that are weak or overpowering in a room.

Compression

• Reduces dynamic range, providing automatic volume control by gauging amplitude change over time, relative to a threshold.
• A 1:1 ratio means no compression occurs.
• Lower ratios have subtle effects.
• Higher ratios result in more aggressive compression.
• Compressor attack time dictates how quickly the compressor begins to attenuate the signal after exceeding the threshold.
• Compressor release time determines how long it takes for the signal to return to its original level after falling below the threshold.
• The "knee" defines how the compressor attenuates signals around the threshold.
• Hard Knee: Applies the full compression ratio instantly once the signal crosses the threshold.
• Soft Knee: Gradually eases the signal into the set ratio over a wider threshold range.

Limiters

• Limiters are compressors with a ratio of 10:1 or greater, effective for blocking sudden peaks.
• Brick wall limiters: Signals never exceed the threshold, feature an infinite ratio, and are used to maximize loudness without clipping, employing an instantaneous attack time.
• A limiter can be placed before a compressor to manage peaks, allowing the compressor to work on the average signal level.

Gates and Expanders

• Key terms for gates and expanders include hold, release, range, and ratio.
• Hold: Duration the gate remains open after the signal drops below the threshold.
• Release: Time it takes for the gate to fully close after the hold time.
• Range: The amount of gain reduction when the gate is fully closed.
• Ratio: Attenuation slope below the threshold.
• Expanders: Dynamic processors that increase the difference between the loudest and quietest parts of an audio signal.
• Expander ratio is applied when a signal falls below a set threshold, which provides a smoother transition than a gate.

Other processors

• De-essers: Narrow-band attenuators targeting sibilance in the 6kHz-8kHz range which can introduce a lisp if overused, and controlled by threshold and target frequency.
• Target frequency: Selects the specific frequency where the de-esser will reduce sibilance.
• Gates: Reduce background noise by opening when the signal crosses a threshold and closing when it falls below it.
• Multi-band compressors: Compress each frequency band independently for precise dynamic control.
• Envelope shapers: Modify the attack and release phases of a sound's gain.

General Terms

• Threshold: The signal level needed to activate a processor.
• Attack Time: How long a processor takes to activate once the threshold is reached.
• Release Time: The time it takes for a processor to deactivate after the signal falls below the threshold.
• Ratio: Attenuation slope above the threshold for compressors, and below the threshold for gates.
• Gain: Output level of the device after processing.
• Side Chain: A filter that influences a device's reaction to the track.
• Key: Using a different track to control a device's processing of another track; used in ducking.
• Amplitude: The strength of a sound wave, perceived as loudness, measured in dB.
• Dynamic Range: The ratio between the loudest and softest signals.
• Dynamics Processor: Automatically controls volume by measuring amplitude change over time via a threshold.
• Compressor becomes a limiter at a ratio of 10:1 or higher.
• Gain reduction exceeding -6 dB may negatively impact sound quality.
• Side chaining involves using one audio track to control the volume of another using a compressor.

Compression vs EQ

• The order of EQ and compression aren't particularly important
• If subtracting EQ can be placed first
• If adding EQ, compression can be placed first and more so fixes a frequency after compression