Music 265B Week 11 Mixing, Part 2
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In the last lesson, we experimented with some basic Signal Processors (plug-ins) like Equalizers (EQ), Compressor/Limiters, Expander/Gates, De-Essers, and Reverb. We used them on our tracks in a few ways. AudioSuite plug-ins let us process the sound of individual clips in the Edit Window, and plug-ins on the Inserts let us affect the entire track. When navigating through the various plug-in menus, you may have noticed a few plug-in categories. Under the Setup > Preferences menu, navigate to the Display tab. In the “Organize Plug-In Menus By:” option, select Category & Manufacturer. This is fairly self-explanatory: the Manufacturer is the company that released the plug-in, like Avid or Digidesign. This can be a useful menu for users with many Third-Party plug-ins: plug-ins from different manufactures, which do not come standard with Pro Tools. Category refers to the different types of plug-ins available to us. Each category processes our sound in different ways. Any Plug-in from any manufacturer, no matter how simple or advanced will fall into one of these categories. Let’s break them down.
An Equalizer (EQ) is a plug-in that raises or lowers the volume of Frequencies within a Bandwidth. In its simplest form, this may consist of some simple Treble (high-frequency) and Bass (low-frequency) gain (volume) knobs, preset to a specific frequency range. A Passive (subtractive) equalizer can only reduce the gain on a frequency band, while an Active EQ can boost and cut.
A Graphic EQ is more elaborate, but follows the same concept as our simple EQ. Graphic units have multiple (several dozen) EQ bands, locked to specific frequency ranges. These multi-band graphic EQ’s are usually used with studio monitors and guitar amplifiers to balance or compensate for the “sound” of the room.
A Parametric EQ is more advanced. These contain multiple EQ bands, with adjustable frequency ranges, referred to as the Q. Parametric equalizers also include a High-Pass Filter (or low-frequency roll-off) and Low-Pass Filter (a high-frequency roll-off). The stock EQ3 7-Band plug-in is a Parametric Equalizer.
Dynamics plug-ins affect the volume and overall dynamic range (the difference between quiet and loud) of our tracks. They include Compressors, Expanders, De-Essers, and others.
Compressors & Limiters restrict the dynamic range of our tracks. While they can raise the overall level of our tracks (making the quietest parts louder), they are primarily used to reduce the loudest peaks in volume (making the loudest parts quieter). When our track gets louder than the compressor/limiter’s Threshold, the plug-in will lower the output by a certain Ratio. For example, when a compressor is set to a 2:1 ratio, if the raw signal would normally peak 2 dB (Decibels) above the threshold, the compressor would only let the signal get 1 dB louder than the threshold, 4 dB would only get 2 dB louder, and so on. A compressor with a very high ratio (e.g. 20:1) is called a Limiter. A Multi-Band Compressor can compress several different frequency ranges in different ways. Heavy compression can make a track sound thicker and generally louder, but extreme compression can make a track sound saturated, or even distorted. Extreme compression can be fatiguing on our ears.
We can use a compressor in several different ways. Normally, we place a compressor plug-in directly on one of our track’s Insert points, like we do with most other plug-ins. However, we can use a signal from a different track to trigger another compressor on our track: Side-Chain Compression. For example, we can place the compressor on our bass track, and create a Send on our kick track to Bus the signal over to our compressor’s Key-Input. Now, whenever kick drum is played, the compressor will activate, and gently bring down the level of our bass: this lets our kick drum pop out in the mix a little bit more.
Another technique is called Parallel Compression. In this case, we duplicate a track’s signal, heavily compress one of the signals, and gently balance the sound of this compressed track against the uncompressed version.
Expanders & Noise Gates work like compressors, but they are used to exaggerate the dynamic range of a track. When a signal gets louder than the expander’s threshold, the expander will boost the gain on those peaks. This in turn makes the loudest parts of a track even louder. A more extreme version of this is a Noise Gate. The gate suppresses the track’s sound until it gets louder than the threshold. When the threshold is crossed, the gate “swings open” allowing the sound to pass through until it closes again. In this case, gates are used to control some of the unwanted background noise in tracks.
A De-Esser tames the Sibilant and Plosive sounds (sharp S, P, T, K and other consonant sounds) in our vocal tracks. The De-Esser combines elements of the EQ & compressor. When a certain Frequency range gets louder than the de-esser’s Threshold, the plug-in will temporarily lower the level of that range. This way, we can preserve the normal high-end brightness of our vocals while taming the unwanted loud parts.
A Channel Strip plug-in combines elements of the Equalization & Dynamics plug-ins into one single plug-in. It may contain an Equalizer, Compressor, Noise Gate, and other filters into one plug-in. Some versions, like Avid’s Channel Strip plug-in allow us to change our FX Chain: the order in which the signal is processed. We may want to equalize the signal before we compress it, or vice versa.
Pitch Shift plug-ins, as the name implies, alter the pitch of a track. This can include plug-ins like Avid’s Pitch, which can Transpose a signal up or down by Semitones & Cents. Popular Third-Party plug-ins like AutoTune and Melodyne are used in Pitch Correction, which attempts to fix the Intonation of a track. We used many of these plug-ins during the end of the editing phase.
Reverb attempts to recreate the way soundwaves get reflected and warped in a Space. When a soundwave radiates out from its source, the wave hits our ears or microphone directly: this is the “dry” sound of the instrument. Since the instrument is played in a room, the same soundwaves eventually bounce and reflect off of the walls. These Reflections continue to Diffuse & Decay in the room, until they eventually reach our ears at different times, depending on the Size and dimensions of the room. The “space” could be a room, hall, church, or chamber of various sizes (small, medium, or large). Reverb can also be created with a metallic device like a metal Spring or Plate. Different spaces and types of reverb have their own unique characteristics.
Rather than inefficiently placing a reverb plug-in on every track in our session, we typically set up a single reverb plug-in on its own channel, using a stereo Aux track. We can then use our Sends to bus the signal over to our reverb channel. This way, we can place our entire band back in the same “room” inside our mix.
Delay plug-ins are used to create an echoing effect. We set up Delay plug-ins using the same technique as our Reverb channel. A classic tape-delay unit used a set length of tape, looped together in one continuous band. The tape would record the incoming signal into a small loop, and play it back when the tape looped back around, with a slight delay. By adjusting the speed of our delay unit, we can cause the delayed sound to land on a steady rhythmic beat, like a quarter note or an 8th note.
Modulation plug-ins contain some of the effects & stomp-boxes found in a guitarist’s pedal board. Most of them operate in the same way: they duplicate our incoming signal, process one of the copies, and blend the two signals back together. A Phase Shifter, or Phaser, uses a sweeping EQ filter to remove some frequencies from our signal, like a guitarist’s Wah-Wah pedal. When the two signals are blended back together, some frequencies cancel each other out, creating a long, rippling effect in the signal. A Flanger uses a short, modulating delay instead of a sweeping EQ. A Chorus uses a longer delay: when the signals are recombined, the sound tries to mimic the vibrato sound of a group of singers (a chorus). A similar effect called a Doubler modulates the pitch & delay of a signal to imitate the minor differences we might find between two separate performances of the same piece. In the end, the doubler makes it sound as though the singer or instrumentalist doubled their performance, even though we only used one take.
Harmonic plug-ins include other guitar pedal effects, like distortion, fuzz, overdrive, and others. Overdrive mimics the sound of a tube guitar amp that has been turned up a little too far. Eventually, the signal gets loud and distorted enough to produce some aesthetically pleasing noise. Fuzz was an early precursor to the distortion pedal: it creates a musically dirty, gravel-like tone. This is the iconic sound of guitarists like Jimmi Hendrix. Distortion takes this tone to extremes. It typically compresses and drives the signal to the point where it makes harsher, but still aesthetically pleasing distortion.
Harmonic plug-ins also include complete guitar & bass amp simulators. This can include everything from pedals & stomp-boxes, to heads & amps, speaker cabinets, rack effects, and even a simulation of different microphones placed around the speaker cone. If we recorded a clean direct signal from the guitar or bass, we can process the signal through one of these simulators.
Noise Reduction plug-ins are some of the specialized tools used in audio restoration. We use these to try to clean up and salvage poorly recorded tracks. Some noise reduction plug-ins attempt to remove clipping & pops, or strip out unwanted buzz & background noise from our tracks.
We use Dither plug-ins during the mastering phase to go from higher bit-depths to lower ones. For example, we may have recorded our session in 32-Bit Float, or 24-Bit for higher audio quality. Eventually, we will mix down to a standard CD format, at 16-Bit. Dithering helps with this conversion process. We’ll cover this during the Mastering phase.
Sound Field plug-ins can include phase scopes, spectrum analyzers, level meters, and other visual tools used to analyze our sound – those tools don’t do anything to change the sound, they just show us what is happening. However, Sound Field plug-ins include a few processors that do alter our signal. Some plug-ins try to shift, alter, and widen a signal within the stereo image (the left & right spectrum). We normally use the Pan knobs to place a sound somewhere within the left or right sound field, but some of these plug-ins can make a track sound “wider” than they really are.
Instrument plug-ins are the virtual synthesizers, drum machines, samplers, and other noise-making modules that we use with MIDI data & Instrument tracks. MIDI provides, the notes, but these plug-ins make the actual sound. Since these Instrument plug-ins are the Sound Source for our MIDI tracks, they should always be placed on the Instrument channel’s first Insert. Other plug-ins, like EQ and compressors should be placed underneath.
Other & Effect
Some categories like Effect and Other can be seen in the list. These are usually plug-ins that can serve multiple functions, or ones that weren’t assigned a specific label (like Equalizer) by the manufacturer. However, it is possible to see one plug-in fall under multiple categories. For example, the Channel Strip is available under both the EQ and Dynamics category.
AudioSuite Utility Plug-Ins
If we click on the AudioSuite menu, we can see an almost identical list of plug-ins. However, we have a few utility plug-ins that we an use to fix some problematic clips, or create new effects. In the AudioSuite menu, navigate to the Other category. Remember, AudioSuite plug-ins will render audio into new clips.
DC Offset Removal will remove any DC offset noise from our clips – that is a loud signal at 0 Hz, usually created by bad audio conversion.
Duplicate will make a new non-destructive copy of the audio clip in the clip list.
Gain will raise or lower the overall volume of the selected clip. This serves the same function as the regular Trim plug-in.
Invert will flip the polarity on a clip. If two tracks are out of phase, this inversion may correct some of the phasing issues.
Normalize will raise or lower all of the peaks in a clip to the same average volume, eliminating the original clip’s dynamic contrast. This works a bit like our dynamics plug-ins, but it can also raise the level on unwanted background noise.
Reverse will render the clip backwards in time. The file will still start at the same time as the original, but all content in the clip will be reversed. To create special effects like a reverse snare hit, simply highlight a snare drum’s hit, from the start of the transient to the end of the wave, and render the clip in reverse. After that, line up the new peak with the original peak to keep the snare in time.
Signal Generator can be used to create different types of sounds, like Sine, Square, Triangle, and Sawtooth waves at any frequency, or White Noise & Pink Noise.
Time Compression Expansion is identical to the TCE time stretching we used earlier in the editing phase. It can, to a certain extent, speed up or slow down clips while maintaining their original intonation.
AudioSuite lets us create a few cool effects like backwards reverb – that is when we hear the sound of the reverb unit before the singer or instrument makes a sound. Using a normal signal flow, there is no way to do this in real-time: it is impossible to do this live. Instead, we can use AudioSuite to perform a few editing functions. Let’s say we wanted to add some backwards reverb to the first word of a phrase for dramatic effect. First, we need to Select the first word or syllable in the phrase and Separate it. Next, we need to highlight that clip, along with a few seconds of “dead air” in front of the clip (the space where we want to the reverb to come in). Next, we Reverse the clip & the dead air, so they play backwards in time. In AudioSuite, we need to find a Reverb plug-in, dial in the right settings, and Render the backwards clip/dead air into one continuous clip. We should now hear the backwards vocal with a long reverb tail after it. If we Reverse it again, we should have a long reverb tail, with a vocal at the end, playing normally. Thankfully, AudioSuite made this task easier on us. The AudioSuite reverb plug-ins have a Reverse button that will perform those functions for us: reversing, rendering, and reversing again.
Continuing to Mix
Where we use plug-ins, and in what order we use them will change the way our tracks sound. AudioSuite plug-ins affect the sound at the Clip level. The sound of these clips are then processed through the Inserts, in order from the first insert to the last. We might use an EQ on the first insert to clean up noise or carve out frequencies we don’t like. Next we may use a compressor on the second insert: the EQed sound gets processed through the compressor. We may decide to use other effects to alter the tone on the next few inserts. Eventually, we may blend this processed signal alongside a reverb or delay unit on a separate track, or process a family of instruments together on a submix.
In our last lesson, we began to alter the EQ & dynamics of our tracks. We learned how to create a reverb bus to efficiently give our tracks the same “room” sound. Now that we have more plug-ins at our disposal, we can shape our tone & texture in new ways. We can add effects to guitars, experiment with delay, and others. For now, we just want to find a nice overall texture for our tracks. In our next lesson, we will focus on blending & balancing our tracks within each section and within the ensemble.