MUS-214-B-Compression Quiz

What is Threshold?

This setting determines the level at which the compressor starts to act. When the audio signal exceeds this level, the compressor reduces the volume. Setting it around the average level of your audio can help smooth out peaks while leaving quieter parts untouched.

What is Ratio?

Controls how much the audio signal is reduced once it exceeds the threshold. For example, a 4:1 ratio means that for every 4 dB over the threshold, the output will only increase by 1 dB. This helps in achieving a more consistent level.

What is Attack?

This setting determines how quickly the compressor responds to the audio signal once it exceeds the threshold. Fast ones can tame sharp peaks and reduce transients, while slower ones allows more transient detail to come through.

What is Release?

This setting controls how quickly the compressor stops reducing the volume after the audio signal falls below the threshold. A fast one can make the audio sound more tightly controlled, while a slower one allows for more natural-sounding dynamics.

What is Makeup Gain?

After compression, the overall volume of the audio might be reduced. This allows you to boost the compressed signal back to a desired level, ensuring that the output is as loud as needed.

What is Knee?

This setting affects how the compressor transitions between non-compression and compression. A hard one means the signal is untouched until it exceeds the threshold, while a soft one gradually applies compression as the signal approaches the threshold.

What is Gain Reduction Meter?

This visual tool shows how much the compressor is reducing the signal's gain. It helps you understand the impact of your settings and make adjustments accordingly.

Compressor Core Concepts

Students should understand:

 ☐ What dynamics are

o The difference between quiet and loud parts of a sound

 ☐ Dynamic range

o The span between the softest and loudest parts of an audio

signal

 ☐ Why compression is used

o To control volume differences

o To make sounds more consistent

o To help sounds sit better in a mix

 ☐ What compression is not

o It does not automatically make audio better

o It does not fix poor performances or recordings

What does a Compressor do (basic level)?

Students should be able to explain:

 ☐ A compressor reduces the level of loud sounds

 ☐ Loud signals are reduced only after they cross a set level

 ☐ Quiet sounds are usually unchanged

 ☐ Compression changes dynamics, not tone (though it may affect

perceived tone)

Essential Compressor Controls (Basic Level)

Students should recognize and define:

Threshold

 ☐ The level at which compression begins

 ☐ Signals below the threshold are unaffected

 ☐ Lower threshold = more compression applied

Ratio

 ☐ How much the signal is reduced after crossing the threshold

 ☐ Example:

o 2:1 = gentle control

o 4:1 = moderate compression

o 8:1+ = heavy compression / limiting

Gain Reduction Meter

 ☐ Shows how much volume is being reduced

 ☐ Measured in decibels (dB)

 ☐ More movement = more compression happening

Compressor Time Controls (intermediate foundation)

Students should understand conceptually:

Attack

 ☐ How quickly compression starts after the signal exceeds the

threshold

 ☐ Fast attack = controls transients (punch, peaks)

 ☐ Slow attack = allows initial hit to pass through

Release

 ☐ How quickly compression stops after the signal falls below the

threshold

 ☐ Fast release = more aggressive, possibly pumping

 ☐ Slow release = smoother, more natural sound

Make-Up Gain / Output Gain

Students should know:

 ☐ Compression often makes audio quieter overall

 ☐ Make-up gain restores perceived loudness

 ☐ Loudness increase ≠ better sound

 ☐ Always compare before and after at equal volume

Listening Skills (Critical for Beginners)

Students should practice identifying:

 ☐ Reduced volume swings

 ☐ More consistent loudness

 ☐ Loss of punch (over-compression)

 ☐ Pumping or breathing artifacts

 ☐ Increased sustain on notes or vocals

Common Beginner Compressor Applications

Students should understand typical use cases:

 ☐ Vocals – control volume changes, improve intelligibility

 ☐ Bass – stabilize low-frequency energy

 ☐ Drums – shape transients and punch

 ☐ Guitars / Keys – smooth uneven performances

Compression vs. Limiting vs. Expansion

Students should be able to distinguish:

 ☐ Compression – reduces loud sounds

 ☐ Limiting – extreme compression to prevent clipping

 ☐ Expansion / Gates – reduce quiet sounds

 ☐ Compressors can behave like limiters at high ratios

Intermediate Compressor Concepts (Conceptual, Not Mastery)

Students should be introduced to:

 ☐ Soft vs. hard knee

o How gradually compression is applied

 ☐ Serial compression

o Using multiple gentle compressors instead of one heavy one

 ☐ Parallel compression (intro only)

o Blending compressed and uncompressed signals

 ☐ Compression order

o Compression before vs. after EQ (conceptual awareness

Common Compressor Mistakes to Avoid

Students should recognize:

 ☐ Compressing everything by default

 ☐ Using extreme ratios without listening

 ☐ Judging sound only by loudness

 ☐ Ignoring gain reduction meters

 ☐ Never bypassing to compare before/after

Basic Workflow Compressor Checklist (Hands-On)

When applying compression, students should:

 ☐ Listen to the track before inserting compression

 ☐ Set threshold so compression only happens when needed

 ☐ Choose a gentle ratio first (2:1–4:1)

 ☐ Adjust attack and release while listening

 ☐ Add make-up gain carefully

 ☐ Bypass often to compare

 ☐ Ask: Does this improve clarity or consistency?

Compression Learning Outcome Summary

By the end of instruction, students should be able to:

 ☐ Explain what compression is and why it’s used

 ☐ Identify key compressor controls

 ☐ Hear basic compression effects

 ☐ Apply gentle compression intentionally

 ☐ Avoid common beginner mistakes

What are the differences between Compressed vs Uncompressed audio?

Uncompressed audio is more volatile and unstable, with higher highs and lower lows; Compressed audio is more streamlined and balanced, with more steady wavelengths.

What does an audio compressor do?

Reduces the volume of the loudest parts of an audio signal and levels out the overall volume variations (dynamic range) of an audio signal. By increasing the output gain (make-up gain) of the compressor, you can make the quieter parts sound louder and closer in volume to the loudest parts.

What is input gain?

Controls the level going into the compressor.

Compressor Ratio

This is the amount of compression applied after the audio signal exceeds the threshold. The higher it is, the more compression is applied. For example:

• If it’s 1:1, there is no compression at all.

• If it’s set at 2:1, for every 2dB the audio signal goes over the threshold, you get 1dB of output above the threshold. When the audio signal exceeds the threshold by 10dB, the compressor reduces the signal 5dB over the threshold.

• If it goes up to 8:1, for every 8 dB of sound over the threshold you will get 1dB of output above the threshold. So if the signal goes over the threshold by 16dB, the compressor reduces the signal to be only 2dB over the threshold.

• If it’s 20:1 to ∞:1 this would be considered “limiting” and can be used to ensure that a signal does not exceed the threshold level.

What is Sidechain?

Refers to a secondary input to a compressor that allows external signals to trigger the compression effect. Instead of the compressor reacting solely to the audio it is processing, it responds to a different signal, often called the "sidechain input."

What are the 4 common compression types?

1. Tube: Probably the oldest type of compression is tube compression. Tube compressors tend to have a slower response — slower attack and release — than other forms of compression. Because of this, tube compressors exhibit a distinct coloration or “vintage” sound that is nearly impossible to achieve with other compressor types.

2. Optical: Optical compressors affect the dynamics of an audio signal via a light element and an optical cell. As the amplitude of an audio signal increases, the light element emits more light, which causes the optical cell to attenuate the amplitude of the output signal.

3. Field Effect Transistor: Referred to as FET, these compressors emulate the tube sound with transistor circuits. They are fast, clean, and reliable. The 1176 is perfect for vocals, bass, guitar and more. It’s also a popular choice for bringing out excitement in room mics.

4. VCA: Fast and punchy VCA compressors run the gamut — from the Rolls-Royce compression of the SSL G Bus or E series used on the mix bus and instrument groups, to the hot-rod attitude of the legendary dbx 160, which can give a snare drum or electric guitar unrelenting character.

What is Dynamic Range?

Refers to the difference (in dB) between the loudest and quietest parts of an audio signal, which a compressor reduces by attenuating peaks exceeding a set threshold. It minimizes the volume gap, creating a more consistent level by lowering loud signals, resulting in a narrower, more controlled range.

What are some basic compressor settings?

Application Attack Release Ratio

Vocals Medium-Fast Slow-Medium 2:1 - 4:1

Electric Guitar Fast Slow 4:1+

Acoustic Guitar Medium Medium 2:1 - 4:1

Drums Fast Fast 2:1- 4:1

Piano Medium Medium-Fast 2:1- 4:1

Bass Fast Medium-Fast 4:1

Brass Fast Slow 4:1

Compressor Tips

1. When in doubt, don’t compress. It can always be added later, but never undone if recorded on the front end. For example, if you have an electric or acoustic guitar part that sits fine in a mix as is, leave it be.

2. If you plan on having your music professionally mastered, avoid putting a compressor on the stereo L/R main bus to compress the entire mix. If you do put compression on your mix (some people like it regardless), send two mixes to your mastering engineer, one with compression and one without. If they can work with your compressed mix and feel that it doesn’t compromise their process (and ultimately your music), then fine. If not, they have what to work with. Don’t use compression solely for the reason of making a mix louder. While many engineers do this, the danger is that an over-compressed mix will lose contrast and will sound dull and boring, losing the listener’s ear. Some mastering engineers actually wind up using expanders (the electronic opposite of compressors) to try to bring back the dynamic range lost by over-compressed mixes.

3. A good way to use stereo bus compression is when you route drum tracks to a stereo bus (not the main L+R) to create a submix. Insert a compressor and an EQ on your stereo bus (this works in hardware and software), squash the drums, boost the highs at 10kHz, lows at 80Hz (leave everything else flat) and send the bus output into two open channels of your mixer. Pan one channel hard left, the other hard right. Now, sneak the drum submix into the mix along with the normal drum tracks so that it widens and reinforces the drums without overtaking them. Congratulations, you have just learned how to create what’s called the "New York" drums sound. This is great for any percussion-driven music, such as rock or hip-hop.

4. To get more snap out of a snare, set an attack time that allows the entire transient to pass. Start with a ratio between 2:1 and 4:1. You’ll need a slower attack time and a fairly quick release. This one requires experimentation. Run your snare track through the compressor starting with the fastest attack possible. You’ll hear a very clipped attack. Now start dialing the attack back (slower) until you hear more of the transient. Don’t be afraid to go beyond the transient and dial back to a faster release until you know that you’re getting just the transient (like setting the water temperature of a shower, where there seems to be only a micro nano-meter between fantastically hot and freezing). Once you have it, set a fast release time. What you’ll hear is the entire attack passing while the sustain portion of the sound dips down for a moment and then rises quickly. This increases the level between transient and sustain giving the illusion of a louder attack combined with a subtle pumping of the snare, which contributes to musical drive.

5. If you’re working with sampled cymbals and want to create a more realistic decay, as though a drummer hit the cymbal and moved on (so to speak), set a longer release time on the compressor. You can adjust the release time to coincide with the next musical event so that there’s not too much overhang, just enough to give the impression that the cymbal is fading of its own accord and not by gating or fixed sample length.

6. Ducking rhythm tracks is another way to use compression. Let’s say you have guitars and synth pads that by themselves sound good and balanced. The bad news is that when the vocals come in, they are fighting to be heard. This technique requires the ability to send a signal to the sidechain of a compressor that will control the volume of the guitars and keyboards. With plug-ins, this is easy if they have sidechain access. Just bus an output from the vocal track to the sidechain key in of the compressors. The rhythm tracks will duck when the vocals come in and go back to normal when the vocals exit. For rhythm tracks, you can use a higher ratio, ranging from 5:1 to 7:1. This also helps to keep them even throughout the song.* Set the threshold so that when the vocals come in, the rhythm tracks simultaneously decrease (or duck) by 2dB to 3dB. Set a fast attack and a long release (1 sec-2 sec). Naturally, you’ll have to adjust the release to suit the music. A fast release time will cause the tracks to pump, which you can also use to your advantage in terms of creating musical drive by adding a subtle pumping to heavy guitars. Again, experiment.

*When you have tracks that need to keep fairly constant in level throughout a song, such as rhythm guitars (clean or distorted), synth pads and backup vocals, it’s okay to use a higher compression ratio. Some engineers will use ratios as high as 5:1, 6:1 and 7:1. As ever, it depends on your tracks. You may choose a lower or even higher ratio depending.*

7. To remove sibilance from vocals and harshness from cymbals, a technique called de-essing is called for. This uses the sidechain input of the compressor and a parametric equalizer. Split the output of the vocal track so that along with your normal main out, you are sending to the equalizer as well. The output of the equalizer will go into the sidechain key input of the compressor. To start, you will be monitoring the EQ only. Usually, vocal sibilance occurs in the range of 3kHz to 8kHz. For cymbals, harsh sounds can occur between 5kHz and 10kHz. We’ll talk about treating vocals, but the technique applies to both. On the equalizer, turn the boost all the way up and sweep through the frequency band (while the vocal track is playing) listening for sibilance (the hissing sound of "s", also "t", "ch", and "sh"). When you find the most obnoxious frequency, set a very narrow Q (bandwidth) so that the compressor will just react to the evil frequency and not squash the good and pure. Leave the signal boosted anywhere from 10dB to 15dB. Now drop in the compressor, and with a high ratio (8:1-10:1), listen to the track. Start with the Threshold set high and then lower it until you hear and see the compressor acting on the sibilance. Gain reduction should show between 3dB and 6dB on the meter. If the compressor is acting on some but not all of the sibilance, the frequency may not be set right or the bandwidth (Q) may be too narrow. Try widening the bandwidth a tad and adjusting the frequency until you get the behavior you’re after. By the way, don’t worry about the oddly EQed vocals, you’re not going to hear them.

Soft Knee vs Hard Knee

Soft Knee smooths out attack, making compression more seamless and natural while Hard Knee is simply the point between uncompressed & compressed audio with no delay.

What are some examples of Compressor settings?

Default Compression Settings

Ratio: 3:1 Threshold: -20 dB Attack: 20-50 ms Release: 100-300ms

Mild Compression (2-3 dB GR)

Good starting point for bus compression or lightly gluing instruments together.

Ratio: 2:1 or 3:1

Threshold: -10 to -20 dB Attack: 10-20 ms Release: 100-200 ms

Medium Compression (4-8 dB GR)

Works well for stronger glue between instruments like drums and guitars. Also used for more transparent control of vocal peaks.

Ratio: 3:1 or 4:1 Threshold: -10 to -15 dB Attack: 10-20 ms Release: 50-100 ms

Heavy Compression (8-12 dB GR)

Slams room mics and drum overheads. Also used for dramatic pumping vocal effects.

Ratio: 8:1 or 10:1 Threshold: -5 dB Attack: <10 ms Release: 75-150 ms