session-architect

Session Architect

Where this fits in the workflow:

1. /phantom:audio-diagnostician -- analyze stems first
2. You are here: /phantom:session-architect -- set up the session
3. /phantom:mix-engineer -- mix with measurement-backed decisions
4. /phantom:effects-engineer -- creative processing
5. /phantom:mastering-engineer -- final output

Philosophy

A well-organized session is half the mix. I've seen engineers waste hours hunting for the right track or untangling routing because they skipped the 15-minute setup. A clean session flows -- you make mixing decisions instead of debugging signal path problems. Color every track, name every bus, route every send before you touch a fader.

If /phantom:audio-diagnostician produced a mix brief, read it first. The stem count, sample rates, problem stems, and masking conflicts all inform how you structure this session. A session built around the diagnostic findings puts the solutions in your signal path from the start.

Session Setup Workflow

Review the mix brief

If audio-diagnostician produced a mix brief, start there. Pull out:

• Stem count and names -- determines your track layout
• Sample rate and bit depth -- set the project to match
• Dealbreaker problems -- stems with phase issues need routing that facilitates polarity flips and time alignment
• Masking conflicts -- knowing that kick and bass fight at 60-100 Hz tells you to set up sidechain routing from the start, not discover you need it mid-mix

If there's no mix brief, gather this information manually before building the session.

Choose a template

Pick the genre template closest to your project from session-templates.md and adapt it. Don't force unconventional projects into a standard template -- start with the closest match and modify. For unusual instrumentation (no drums, orchestral instruments, synth percussion), start from the rock/metal template (the most comprehensive) and strip out what you don't need, rename what doesn't fit.

Create the track hierarchy

Reaper's folder tracks serve double duty: visual grouping AND audio bus. A track set as a folder automatically sums its children -- put your compressor on the folder track and it's a bus compressor. This is Reaper's superpower and the foundation of every session.

Standard bus architecture (adapt per genre):

DRUMS (folder/bus) -- color: red
  Kick In
  Kick Out
  Snare Top
  Snare Bottom
  Hi-Hat
  Toms (1, 2, 3)
  Overhead L, Overhead R
  Room L, Room R

BASS (folder/bus) -- color: blue
  Bass DI
  Bass Amp (if present)

GUITARS (folder/bus) -- color: green
  Rhythm L, Rhythm R
  Lead
  Clean / Acoustic

VOCALS (folder/bus) -- color: yellow
  Lead Vocal
  Harmonies
  Backing Vocals
  Ad-libs

KEYS / SYNTHS (folder/bus) -- color: orange
  Piano, Organ, Synth Pad, Synth Lead

FX RETURNS (folder/bus) -- color: purple
  Room Verb
  Plate Verb
  Slapback Delay
  Long Delay
  Parallel Compression

MIX BUS (master parent)

Requires a Reaper MCP server. Automated track creation, folder setup, and color assignment need a Reaper MCP server connected. See the setup guide for installation. Without it, use this as a reference for manual session setup in Reaper.

Set up auxiliary channels

Reverb sends:

• Room reverb (short, natural) -- primarily for drums
• Plate reverb (medium, vocal-focused) -- vocals, snare, sometimes guitars
• Hall reverb (long, cinematic) -- for special moments, strings, pads

Delay sends:

• Slapback delay (50-120 ms, single repeat) -- vocal thickening, rockabilly guitar
• Long delay (quarter note or dotted eighth, 3-5 repeats with feedback) -- vocal phrases, guitar leads

Parallel compression:

• Parallel drum bus -- heavy compression (10:1+), blend underneath the dry drum bus
• Parallel vocal bus -- aggressive compression for density, blend at -10 to -6 dB

All send levels start at -inf (negative infinity). Bring up to taste during mixing. Never set sends at 0 dB as a starting point -- that's the maximum, not the default.

Configure sidechain routing

Sidechain bass to kick is the most common sidechain setup. In Reaper, sidechain signals travel on channels 3-4 (the first pair beyond the main stereo out on channels 1-2).

How to set up sidechain in Reaper:

1. On the kick track, add a send to the bass track
2. Set the send to channels 3-4 (not 1-2)
3. On the bass track's compressor (ReaComp), set the sidechain input to channels 3-4
4. The compressor now responds to the kick signal while processing the bass audio

This makes the bass duck briefly when the kick hits -- creating space in the low end without EQ. For frequency-dependent sidechaining, HPF the sidechain input at 80-100 Hz so only the sub frequencies duck (not the kick's attack).

Other common sidechain setups:

• Synth pad sidechained to vocal (gentle ducking for vocal clarity)
• Rhythm guitar sidechained to vocal (duck 1-2 dB during vocal phrases)
• Reverb return sidechained to dry source (ducked reverb for clarity)

Color coding and naming

Consistency matters more than the specific scheme. Pick colors per instrument group and stick with them across all sessions:

Group	Color	Why
Drums	Red	High energy, attention-grabbing -- drums are the foundation
Bass	Blue	Cool, low -- visually opposite to drums
Guitars	Green	Middle ground, organic
Vocals	Yellow	Bright, stands out -- vocals should always be easy to find
Keys/Synths	Orange	Warm, between guitars and vocals
FX Returns	Purple	Distinct from all instrument groups

Name tracks descriptively: "Kick In" not "Audio 1", "Lead Vox" not "Track 14". When you come back to a session after a week, the names should tell you exactly what each track is without soloing.

Reaper MCP Reliability Notes

When building sessions through the Reaper MCP:

• Always set track names explicitly with set_track_name after insert_track — the name parameter on insert is unreliable
• Verify audio landed on the correct track after each insert_audio_file call — check with get_track_items
• Check FX indices after deletions — deleting a track shifts all subsequent track indices. Always re-query get_project_summary after structural changes
• iZotope plugins need modules added through their GUI — Ozone 11 starts empty even when MCP params are set. The user must add modules (EQ, Imager, Dynamics, Maximizer) through Ozone's interface before params take effect
• Verify param values after setting — some plugins have internal linking that overrides MCP-set values. Always read back critical params to confirm they held

Render settings

Set the project sample rate to match the stems (don't let Reaper resample on import). Internal processing: 32-bit float (Reaper's default, leave it).

Deliverable	Format	Sample Rate	Bit Depth	Notes
Stems for mixing	WAV	Match project	32-bit float	Preserves full dynamic range
Mix for mastering	WAV	Match project	24-bit	Standard delivery to mastering
Preview / client approval	MP3	44.1 kHz	320 kbps	Lossy but good enough for review
Apple Digital Masters	WAV	96 kHz (if source supports)	24-bit	Submit highest quality available

Gain staging

Before any processing, set all faders to unity (0 dB) and check levels. Aim for -18 dBFS average on each channel -- this gives plugins the headroom they expect (most plugin emulations are calibrated to -18 dBFS = 0 VU). If a stem is significantly hotter or quieter, use the item/clip gain (not the fader) to bring it to the right level.

Automation Setup

Envelopes are how you make a mix breathe. Set them up during session creation so they're ready when you need them.

Essential envelope types:

• Volume -- the most powerful mixing tool. Word-by-word vocal riding, section dynamics
• Pan -- rarely automated, but useful for stereo effects and movement
• Mute -- clean transitions, removing noise between phrases
• Send level -- delay throws (punch send to 0 dB on the last word of a phrase), reverb swells
• FX parameters -- filter sweeps, drive changes, EQ automation

Automation modes:

• Trim/Read -- reads existing automation, fader trims on top (default, start here)
• Touch -- writes while you touch the fader, returns to previous value on release
• Latch -- writes while you touch, holds the last value after release
• Write -- overwrites everything, destructive (use sparingly)

Reaper-Specific Knowledge

For detailed Reaper track, bus, plugin, and routing setup, see reaper-setup.md.

This covers:

• Folder tracks as buses (dual-purpose architecture)
• 64 internal audio channels and sidechain routing
• Built-in plugin reference (ReaEQ, ReaComp, ReaXcomp, ReaGate, ReaFIR, ReaDelay, ReaVerbate, ReaLimit)
• SWS Extensions and ReaPack
• Render settings for all delivery formats

Genre Templates

For genre-specific session templates (track layouts, routing conventions, color schemes), see session-templates.md.

Available templates:

• Rock/Metal (most comprehensive -- use as starting point for unusual projects)
• Pop
• Hip-Hop/Trap
• Electronic/EDM
• Acoustic/Folk

Reaper DAW Recipes

For compound Reaper operations that apply this skill's methodology, see reaper-recipes.md.

Available recipes:

• setup_metal_session -- creates rock/metal session from template
• setup_pop_session -- creates pop session from template
• setup_hiphop_session -- creates hip-hop/trap session from template
• setup_electronic_session -- creates electronic/EDM session from template
• setup_from_diagnostic -- adapts template based on diagnostic findings

Recipes require a Reaper MCP server (TwelveTake recommended). See setup guide for installation.