11.4 Parallel Compression and Bus Compression

Parallel and bus compression are powerful tools in dynamic processing, enhancing mix cohesion and punch. These techniques blend compressed and uncompressed signals, allowing for precise control over the balance between transient impact and sustained energy.

When applied thoughtfully, parallel and bus compression can create a more consistent and powerful sound while maintaining natural dynamics. They're particularly effective on drums, vocals, and bass, but can be used on any mix element to add depth and polish.

Parallel compression for depth and punch

Concept and benefits of parallel compression

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• Parallel compression blends compressed and uncompressed versions of the same audio signal (New York compression)
• Preserves transients and dynamics while adding sustain and density to the sound
• Applicable to individual tracks, groups of instruments, or entire mix
• Increases perceived loudness, enhances punch, and improves clarity without sacrificing original dynamics
• Particularly effective on drums, vocals, and bass, but usable on any mix element
• Achievable through aux sends, duplicate tracks, or dedicated parallel compression plugins
• Ratio between dry and compressed signals determines overall effect and adjustable to taste
• Creates a more consistent and powerful sound while maintaining natural dynamics
• Allows for precise control over the balance between transient impact and sustained energy
• Can help elements sit better in a mix by adding body and presence without overpowering other instruments

Implementation techniques

• Set up parallel compression chain using aux sends or by duplicating tracks in DAW
• Apply compressor with high ratio (8:1 or higher) and fast attack and release times to parallel channel
• Adjust threshold for significant gain reduction (10-20 dB) on parallel channel
• Blend compressed signal with dry signal, starting at low level and increasing to taste
• Use make-up gain on compressed channel to match levels and enhance effect
• Experiment with different compressor types for varying tonal characteristics (VCA, FET, optical)
• Consider using multiband compression in parallel for more precise control over specific frequency ranges
• Try different compression curves (soft knee, hard knee) to shape the character of the parallel compression
• Experiment with pre-EQ on the parallel channel to emphasize specific frequencies before compression
• Use parallel compression to add excitement to specific frequency ranges (bass boost, midrange presence)

Bus compression for cohesion and glue

Understanding bus compression

• Bus compression applies compression to a group of tracks or entire mix
• Primary goal creates sense of cohesion and "glue" between different mix elements
• Applicable to instrument groups (drums, backing vocals) or master bus for overall mix cohesion
• Typically uses lower ratios (2:1 to 4:1) and gentler gain reduction (2-6 dB) compared to individual track compression
• Attack and release times significantly influence overall sound and groove of the mix
• Enhances perceived loudness and density without resorting to excessive limiting
• Popular hardware-modeled plugins include SSL G-Bus, API 2500, and Fairchild 670
• Helps create a more polished and professional-sounding mix
• Can add subtle harmonic distortion and character to the overall sound
• Useful for controlling dynamic range and creating a more consistent mix across different playback systems

Application techniques

• Apply bus compression to subgroups (drums, vocals, guitars) to create cohesion within instrument families
• Use on the master bus to glue the entire mix together and add final polish
• Experiment with different compressor models to find the right character for your mix
• Consider using multiple stages of bus compression (subgroups and master) for more control
• Utilize parallel bus compression to blend compressed and uncompressed signals for added flexibility
• Try different compressor circuit types (VCA, FET, Variable-mu) to achieve varying tonal colors
• Use bus compression in conjunction with individual track compression for a layered approach to dynamics control
• Experiment with mid/side bus compression to affect the center and sides of the stereo image differently
• Consider using multiband bus compression to target specific frequency ranges for more precise control
• Automate bus compressor parameters to adapt to different sections of the song

Bus compressor settings for dynamics and unity

Setting up bus compression

• Start with low ratio (2:1 or 3:1) to maintain natural dynamics while achieving cohesion
• Set relatively slow attack time (10-30 ms) to allow transients to pass through, preserving punch and impact
• Adjust release time to complement tempo and groove of music, typically between 50-300 ms
• Use threshold to achieve gentle gain reduction, aiming for 2-4 dB of compression on loudest parts
• Experiment with different compression knee settings to find right balance between transparency and character
• Utilize compressor's sidechain high-pass filter to prevent low frequencies from dominating compression
• Consider using manual gain riding or automation in conjunction with bus compression for more precise dynamic control
• Start with a low mix or wet/dry balance and increase gradually to find the sweet spot
• Use metering tools to visualize the amount of gain reduction and ensure consistency across the mix
• Listen for changes in stereo image and adjust accordingly to maintain proper balance

Fine-tuning and advanced techniques

• Use bus compression in conjunction with individual track compression for layered approach to dynamics control
• Experiment with different attack shapes (linear, logarithmic) to shape transient response
• Try using bus compression as a form of soft limiting to catch peaks without squashing the overall mix
• Adjust the compressor's internal sidechain EQ to focus on specific frequency ranges for more targeted compression
• Use bus compression to enhance the groove of the mix by emphasizing rhythmic elements
• Experiment with different compressor models on different buses to add variety and character to the mix
• Consider using dynamic EQ in conjunction with bus compression for more precise frequency-dependent control
• Try using bus compression in M/S mode to affect the mono and stereo content differently
• Experiment with vintage-style bus compressors to add analog warmth and character to digital recordings
• Use bus compression to create a sense of front-to-back depth in the mix by compressing background elements more heavily