name	Audio Mixing & Mastering
tier	3
load_policy	task-specific
description	Mix voice, binaural, and SFX stems into final master
version	1.0.0
parent_skill	production-operations

Audio Mixing Skill

The Mix Is Where Magic Happens

This skill handles combining voice, binaural beats, and sound effects into a cohesive, hypnotic audio experience.

Purpose

Mix multiple audio stems at correct levels and apply hypnotic post-processing for production masters.

Standard Stem Levels

CRITICAL: Always use these exact levels.

Stem	Level	Rationale
Voice	-6 dB	Reference level, prevents clipping
Binaural	-6 dB	Audible but not distracting
SFX	0 dB	Full impact for transitions

Canonical Mix Command

ffmpeg -y \
  -i sessions/{session}/output/voice_enhanced.wav \
  -i sessions/{session}/output/binaural_dynamic.wav \
  -i sessions/{session}/output/sfx_track.wav \
  -filter_complex \
    "[0:a]volume=-6dB[voice]; \
     [1:a]volume=-6dB[bin]; \
     [2:a]volume=0dB[sfx]; \
     [voice][bin][sfx]amix=inputs=3:duration=longest:normalize=0[mixed]" \
  -map "[mixed]" \
  -acodec pcm_s16le \
  sessions/{session}/output/session_mixed.wav

Important: Use normalize=0 to prevent unpredictable level changes.

Input Stems

Stem	File	Required
Voice	`voice_enhanced.wav`	Yes
Binaural	`binaural_dynamic.wav`	Yes
SFX	`sfx_track.wav`	Optional

Never use voice.mp3 - always use the enhanced version.

Hypnotic Post-Processing (MANDATORY)

After mixing, apply psychoacoustic mastering:

python3 scripts/core/hypnotic_post_process.py --session sessions/{session}/

Triple-Layer Hypnotic Presence

Layer	Enhancement	Level	Effect
1	Whisper Overlay	-22 dB	Ethereal presence
2	Subharmonic	-12 dB	Grounding presence
3	Double-Voice	-14 dB, 8ms delay	Subliminal presence

Additional Enhancements

Enhancement	Description	Default
Tape Warmth	Analog saturation	25% drive
De-essing	Sibilance reduction	4-8 kHz
Room Tone	Gentle reverb	4% wet
Cuddle Waves	Amplitude modulation	0.05 Hz, ±1.5 dB
Echo	Subtle depth	180ms, 25% decay

Output Files

File	Purpose
`session_mixed.wav`	Pre-master mix (intermediate)
`{session}_MASTER.mp3`	Final deliverable (320 kbps)
`{session}_MASTER.wav`	Archive master (24-bit)

Two-Stem Mix (No SFX)

When no SFX track is needed:

ffmpeg -y \
  -i sessions/{session}/output/voice_enhanced.wav \
  -i sessions/{session}/output/binaural_dynamic.wav \
  -filter_complex \
    "[0:a]volume=-6dB[voice]; \
     [1:a]volume=-6dB[bin]; \
     [voice][bin]amix=inputs=2:duration=longest:normalize=0[mixed]" \
  -map "[mixed]" \
  -acodec pcm_s16le \
  sessions/{session}/output/session_mixed.wav

Level Verification

After mixing, check levels:

# Check peak level (should be < 0 dB)
ffmpeg -i session_mixed.wav -af "volumedetect" -f null /dev/null 2>&1 | grep max_volume

# Check LUFS (target: -14 LUFS)
ffmpeg -i session_mixed.wav -af "loudnorm=print_format=json" -f null /dev/null 2>&1

Target Levels

Metric	Target	Acceptable Range
Integrated LUFS	-14 LUFS	-16 to -12 LUFS
True Peak	-1.5 dBTP	< -1.0 dBTP
Peak	-3 dB	< 0 dB

Binaural Beat Standards

Brainwave State	Frequency Range	Use For
Beta	13-30 Hz	Alert, focused
Alpha	8-12 Hz	Relaxed, light trance
Theta	4-7 Hz	Deep trance, meditation
Delta	0.5-3 Hz	Very deep, sleep-adjacent

Typical Journey Curve

0:00  - Alpha (10 Hz) - Induction
5:00  - Theta (7 Hz)  - Deepening
15:00 - Deep Theta (4 Hz) - Journey core
25:00 - Theta (7 Hz)  - Integration
28:00 - Alpha (10 Hz) - Emergence

Troubleshooting

Issue	Cause	Solution
Clipping/distortion	Levels too hot	Check stem levels, use -6 dB
Binaural inaudible	Level too low	Should be -6 dB (not -12 dB)
Voice buried	Binaural too loud	Verify -6 dB on binaural
Muddy mix	Sample rate mismatch	All stems same rate (44100 or 48000)
SFX too harsh	Level too high	Try -3 dB for gentler SFX
Silent output	normalize=1 issue	Use `normalize=0` in amix

Quality Checklist

Before video assembly:

{session}_MASTER.mp3 exists
No clipping or distortion
Binaural beats audible but not intrusive
Voice clear and present
SFX properly timed (if used)
LUFS within target range
Duration matches expected

Integration with Pipeline

Before (dependencies):

Voice synthesis complete (voice_enhanced.wav)
Binaural generated (binaural_dynamic.wav)
SFX track if needed (sfx_track.wav)

After (next steps):

Video assembly
YouTube packaging

Related Resources

Skill: tier3-production/voice-synthesis/ (input)
Skill: tier3-production/video-assembly/ (next step)
Serena Memory: audio_production_methodology
Script: scripts/core/hypnotic_post_process.py

Audio Mixing & Mastering

Install Skill

SKILL.md