3.5 Audio mixing techniques

Audio mixing is a crucial skill in TV production. It involves balancing sound levels, adjusting frequencies, and applying effects to create a polished final product. Understanding the layout of mixing consoles, gain staging, and signal flow is essential for effective audio control.

Mastering EQ techniques, dynamic range processing, and time-based effects allows producers to shape the sound to fit their vision. Live mixing requires quick thinking, while post-production offers more precision. Proper stereo mixing and loudness management ensure the audio translates well across different playback systems.

Audio mixing console layout

• Audio mixing consoles are the central hub for routing, processing, and blending audio signals in a studio or live sound environment
• The layout of a mixing console is designed to provide intuitive access to all the necessary controls for shaping individual channels and the overall mix
• Understanding the organization and function of each section is essential for efficient and effective audio mixing

Channel strip components

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• Mic preamp: Amplifies low-level signals from microphones to line-level for further processing
• EQ section: Allows tonal shaping of individual channels with high and low pass filters, parametric or graphic EQs
• Aux sends: Routes channel signal to external effects processors or monitor mixes
• Pan pot: Positions the channel in the stereo field (left-right)
• Fader: Adjusts the volume level of the channel

Master section controls

• Main faders: Control the overall level of the stereo mix bus
• Matrix outputs: Provide additional mix buses for sending to multiple destinations (recording, broadcast, etc.)
• Talkback: Allows the engineer to communicate with performers via the studio monitors or headphones
• Monitor controls: Manage the level and source of the control room monitors

Auxiliary sends and returns

• Pre/post fader: Determines whether the aux send level is affected by the channel fader (post) or independent (pre)
• Effects returns: Receives the processed signal from external effects units and blends it back into the mix
• Headphone feeds: Dedicates aux mixes to create custom headphone mixes for performers

Gain staging

• Gain staging is the process of setting appropriate levels at each stage of the signal path to maintain optimal signal-to-noise ratio and avoid clipping
• Proper gain structure ensures the best possible audio quality and minimizes noise and distortion
• Gain staging involves balancing the levels of the mic preamp, channel fader, and master fader

Mic preamp levels

• Set the preamp gain to achieve a strong, clean signal without clipping
• Aim for peak levels around -18 to -12 dBFS (decibels below full scale) to leave headroom for processing
• Avoid setting the preamp too low, as this can introduce noise when raising the channel fader

Channel fader levels

• Adjust channel faders to balance the relative levels of each track in the mix
• Use the faders to create a rough mix before applying processing (EQ, compression, etc.)
• Keep faders within a reasonable range (e.g., -10 to +10 dB) to maintain control and avoid drastic level changes

Master fader level

• Set the master fader to unity gain (0 dB) as a starting point
• Make fine adjustments to the master fader to achieve the desired overall mix level
• Ensure the master level does not exceed 0 dBFS to prevent clipping in the final output

Signal flow in mixing

• Understanding the path an audio signal takes through the mixing console is crucial for troubleshooting and creative control
• Signal flow involves routing input sources to channels, applying processing, and summing to the main mix bus
• Visualizing the signal flow helps in identifying where to make adjustments and insert effects

Input sources to channels

• Microphones, instruments, and line-level sources are connected to the console's input jacks
• Each input is assigned to a corresponding channel strip for individual processing and level control
• Direct outputs allow the recording of individual channels before they are affected by the mix bus

Channel processing order

• The typical processing order in a channel strip is: mic preamp, high-pass filter, EQ, compressor/gate, aux sends, pan, fader
• This order allows for logical and efficient signal shaping, with dynamics control after EQ and before level adjustments
• Some consoles offer flexible signal routing options to customize the processing order

Main mix bus

• The main mix bus is where all the individual channels are summed together to create the stereo mix
• Insert points on the main mix bus allow for the addition of master processing (EQ, compression, limiting)
• The main mix bus feeds the master fader and ultimately the main outputs of the console

Equalizer (EQ) techniques

• EQ is used to shape the tonal balance of individual channels and the overall mix
• Different types of EQs (filters, parametric, graphic) offer various ways to boost or cut specific frequency ranges
• Understanding the frequency characteristics of different instruments and voices helps in making informed EQ decisions

Low and high pass filters

• High-pass filters (HPFs) remove low frequencies below a set cutoff point, useful for reducing rumble, plosives, and proximity effect
• Low-pass filters (LPFs) remove high frequencies above a set cutoff point, helpful in taming harshness or sibilance
• Filters with adjustable slopes (6 dB/oct, 12 dB/oct) allow for more precise control over the cutoff characteristics

Parametric vs graphic EQ

• Parametric EQs offer continuous control over frequency, gain, and Q (bandwidth) for each band
• Graphic EQs have fixed frequency bands with slider controls for gain adjustments
• Parametric EQs are more surgical and precise, while graphic EQs are better suited for broad tonal shaping

Frequency ranges for instruments

• Kick drum: 60-100 Hz (fundamental), 2-4 kHz (attack)
• Snare drum: 200-250 Hz (body), 5-7 kHz (snap)
• Electric guitar: 200-400 Hz (warmth), 2-5 kHz (presence)
• Male vocals: 100-200 Hz (fullness), 2-4 kHz (clarity), 8-10 kHz (air)
• Female vocals: 200-400 Hz (body), 4-6 kHz (presence), 10-12 kHz (brilliance)

Dynamic range processing

• Dynamic range processors (compressors, limiters, expanders, gates) control the volume variations in an audio signal
• These tools help to manage the balance between loud and soft parts, create consistency, and prevent clipping
• Understanding the different types of processors and their parameters is essential for effective dynamic range control

Compressors and limiters

• Compressors reduce the dynamic range by attenuating signals above a set threshold level
• Ratio, attack, release, and makeup gain are key parameters in shaping the compression characteristics
• Limiters are compressors with high ratios (10:1 or higher) used to prevent peaks from exceeding a set threshold

Expanders and gates

• Expanders increase the dynamic range by attenuating signals below a set threshold level
• Expanders are useful for reducing noise and increasing the apparent contrast between soft and loud parts
• Gates are expanders with high ratios that completely mute signals below the threshold, helpful for removing unwanted background noise

Sidechain triggering

• Sidechain allows an external signal to control the compression or gating of another signal
• Ducking is a common sidechain technique where a narrator's voice triggers compression on the background music
• Sidechain EQ can be used to make the compressor more sensitive to specific frequency ranges (e.g., de-essing)

Time-based effects in mixing

• Time-based effects (reverb, delay, modulation) add depth, space, and movement to audio signals
• These effects can enhance the perceived size of a sound, create a sense of ambience, or add creative textures
• Understanding the different types of time-based effects and their parameters is crucial for creating polished and engaging mixes

Reverb types and parameters

• Hall, room, plate, and spring are common reverb algorithms that simulate different acoustic spaces
• Pre-delay, decay time, and diffusion are key parameters in shaping the reverb character
• EQ and damping controls allow for tonal shaping of the reverb tail

Delay techniques

• Simple delay repeats the input signal at a set time interval, creating an echo effect
• Ping-pong delay alternates the repeats between the left and right channels for a wide stereo effect
• Feedback control determines the number of repeats, while mix sets the balance between dry and wet signals

Modulation effects

• Chorus creates a thickening effect by combining the original signal with slightly detuned and delayed copies
• Flanger produces a sweeping, jet-like sound by mixing the input with a short, modulated delay
• Phaser creates a swirling effect by using all-pass filters to introduce phase cancellation at specific frequencies

Aux sends for monitor mixes

• Aux sends allow the creation of separate mixes for musicians' headphones or stage monitors
• These mixes provide performers with a tailored blend of instruments and vocals to help them perform their best
• Proper use of aux sends is essential for ensuring a comfortable and feedback-free monitoring environment

Pre vs post fader sends

• Pre-fader sends are not affected by the channel fader, ensuring a consistent monitor mix regardless of fader moves
• Post-fader sends follow the channel fader, allowing the monitor mix to change with fader adjustments
• Pre-fader sends are typically used for monitor mixes, while post-fader sends are used for effects sends

Headphone mix considerations

• Each musician may have different preferences for the balance of instruments and vocals in their headphones
• Use aux sends to create custom headphone mixes that cater to individual needs
• Provide a balance of the musician's own instrument, key accompaniment, and a reference of the overall mix

Feedback prevention strategies

• Feedback occurs when a monitor speaker is picked up by a nearby microphone, creating a loop
• Position monitors away from microphones and aim them directly at the performer's ears
• Use EQ to identify and cut the specific frequencies that are prone to feedback in each monitor mix

Mixing live vs in post-production

• Live mixing involves making real-time adjustments to balance and shape the sound for an audience
• Post-production mixing allows for more detailed and precise control over individual tracks in a studio environment
• Understanding the differences between live and post-production mixing is important for adapting techniques to each situation

Real-time adjustments and automation

• In live mixing, the engineer must make quick decisions and adjust levels, EQ, and effects on the fly
• Mixing consoles with scene recall and automation features can help manage complex live mixes
• Effective use of fader layers, VCAs, and subgroups can simplify the control of multiple channels

Offline processing advantages

• Post-production mixing allows for non-destructive, offline processing of individual tracks
• Edits, fades, and complex automation moves can be performed with greater precision and flexibility
• Plug-in effects and virtual instruments can be used to enhance and manipulate the recorded audio

Deliverable file formats

• Live mixes are typically delivered as stereo or multi-channel audio files for immediate playback or broadcast
• Post-production mixes may be delivered as stereo files, stems (subgroups), or multi-channel formats (5.1, 7.1)
• Common audio file formats for delivery include WAV, AIFF, and MP3 (compressed)

Stereo mixing principles

• Stereo mixing involves the placement and balance of elements in a two-channel (left-right) sound field
• Proper use of panning, stereo width, and mono compatibility is essential for creating engaging and translatable mixes
• Understanding stereo mixing principles helps in crafting mixes that sound great on a variety of playback systems

Panning for stereo width

• Panning determines the left-right position of a sound in the stereo field
• Wide panning can create a sense of space and separation between instruments
• Avoid hard panning (100% left or right) for most elements to maintain a balanced and cohesive mix

Mono compatibility issues

• Mono compatibility refers to how a stereo mix translates when played back on a single speaker
• Phase cancellation can occur when stereo elements are summed to mono, resulting in a thin or hollow sound
• Check mono compatibility regularly and make adjustments to minimize phase issues (e.g., avoid excessive stereo widening)

Mid-side (M/S) processing

• Mid-side processing separates a stereo signal into its mono (mid) and stereo (side) components
• M/S processing allows for independent control over the center and sides of the stereo image
• Techniques like M/S EQ and compression can help to enhance clarity, width, and punch in a mix

Loudness and dynamic range

• Loudness refers to the perceived volume of an audio signal, while dynamic range is the difference between the loudest and softest parts
• Proper management of loudness and dynamic range is crucial for creating mixes that are both impactful and comfortable to listen to
• Understanding metering, normalization standards, and the requirements for different playback environments is essential for optimizing loudness and dynamic range

Peak vs RMS metering

• Peak meters display the instantaneous level of an audio signal, showing the highest amplitude reached
• RMS (root mean square) meters show the average level over a short time window, better representing perceived loudness
• Use peak meters to avoid clipping and RMS meters to gauge overall loudness and make level adjustments

Loudness normalization standards

• Loudness normalization aims to achieve consistent perceived loudness across different audio content
• Standards like EBU R128 and ITU-R BS.1770 define measurement methods and target levels for broadcast and streaming
• Mixing with loudness meters (e.g., LUFS) helps to ensure compliance with normalization standards

Dynamic range for broadcast

• Broadcast audio requires a controlled dynamic range to ensure consistent loudness and prevent overloading transmission systems
• Dynamic range compression and limiting are used to reduce the difference between loud and soft parts
• Aim for a dynamic range of around 8-12 dB for broadcast mixes, while preserving some natural variation for impact and clarity