Reaper Mastering Guide: Professional Mastering with Stock Plugins

Mastering is the final step between your mix and a release-ready audio file. It is the process of taking a stereo mix and optimizing it for loudness, tonal balance, stereo width, and format compatibility. In Reaper, every tool you need for professional mastering ships with the $60 license. ReaEQ handles corrective and tonal equalization. ReaXcomp delivers multiband compression. ReaLimit provides true peak brickwall limiting. JSFX plugins offer stereo imaging, metering, and utility functions. No third-party purchases required.

For beat battle producers, mastering is the difference between a beat that sounds good in your headphones and a beat that hits hard through the Audeobox playback system. A properly mastered beat translates across phone speakers, earbuds, laptop speakers, and studio monitors. This guide walks through the complete mastering process using only Reaper's built-in tools.

What Is Mastering and Why It Matters

Mastering serves three purposes:

1. Tonal correction - Fix any broad frequency imbalances in the mix that you missed during mixing
2. Dynamic optimization - Control the overall dynamic range so the track sounds consistent from quiet to loud sections
3. Loudness maximization - Bring the track to competitive loudness levels without introducing distortion or squashing dynamics

Mastering is not mixing. If your mix has problems (muddy bass, harsh highs, unbalanced levels), go back and fix the mix. Mastering enhances a good mix. It cannot fix a bad one. The mastering chain amplifies everything in the mix, including problems.

Mastering Session Setup in Reaper

Creating a Mastering Project

1. Export your final mix as a stereo WAV file: 24-bit, 44.1 kHz (or the sample rate you mixed at). Do not apply any limiting or master bus processing during export. Export the mix clean.
2. Open a new Reaper project. Set the sample rate to match your export (44.1 kHz).
3. Import your mix file by dragging it into the arrange view. It creates a single track with one Item.
4. Create a reference track below it. Import a professionally mastered track in a similar style for comparison.
5. Route the reference track directly to your hardware output, bypassing the master bus. This ensures master processing only affects your mix, not the reference.

The Mastering FX Chain

Build your mastering chain on the Master track's FX Chain in this order:

1. ReaEQ (corrective EQ)
2. ReaXcomp (multiband compression)
3. ReaEQ (tonal shaping EQ, optional second instance)
4. JSFX Stereo Width (stereo imaging)
5. ReaLimit (final limiter)
6. JS: Loudness Meter (monitoring, no processing)

Every plugin in this chain processes the full stereo mix. The order matters: EQ before compression ensures the compressor reacts to the corrected frequency balance. The limiter goes last to catch any peaks from the preceding processing.

Mastering EQ with ReaEQ

Mastering EQ is about broad strokes, not surgical cuts. You are shaping the overall tonal balance of the mix, not fixing individual elements.

Corrective EQ (First Instance)

• High-pass filter at 20-30 Hz: Remove sub-sonic content that consumes headroom without being audible. Use a gentle slope (6 or 12 dB/octave) to avoid affecting the audible bass.
• Low-end check (40-100 Hz): Compare your bass weight to the reference track. If your mix sounds thin, a 1-2 dB shelf boost at 60 Hz adds weight. If it sounds boomy, a 1-2 dB cut in the same range cleans it up.
• Mud check (200-400 Hz): A broad 1-2 dB cut here clears up accumulated mud that individual track high-passes did not fully address.
• Presence check (2-5 kHz): If the mix sounds dull or distant, a gentle 1-2 dB boost in this range brings it forward. If it sounds harsh, a 1 dB cut smooths it out.
• Air shelf (10-16 kHz): A high shelf boost of 1-2 dB adds openness and shimmer. Apply this last and check on multiple playback systems.

The key discipline: no mastering EQ move should exceed 3 dB. If you need more than 3 dB of correction at any frequency, the mix needs work, not the master.

Multiband Compression with ReaXcomp

ReaXcomp splits the audio into frequency bands and compresses each independently. This lets you control the dynamics of the bass without affecting the highs, tighten the mids without squashing the lows, and manage the top end without pulling down the body of the mix.

Setting Up ReaXcomp for Mastering

1. Insert ReaXcomp on the Master track after ReaEQ.
2. Configure three bands:
   • Low band: 0-200 Hz (bass and sub-bass)
   • Mid band: 200 Hz - 5 kHz (body, presence, vocals)
   • High band: 5 kHz - 20 kHz (air, cymbals, brightness)
3. Set each band's ratio to 1.5:1 to 2:1. Mastering compression is gentle. Ratios above 3:1 are almost never appropriate for mastering.
4. Set attack times to 10-30ms across all bands. This lets transients pass through before compression engages.
5. Set release times to Auto or 100-200ms. The auto-release adapts to the musical content.
6. Adjust thresholds so each band shows 1-3 dB of gain reduction at most. You should barely be touching the signal.

Band-Specific Considerations

• Low band: The bass region carries the most energy. Compress it gently to even out 808 sustain and kick punch without making the low end feel squashed. If the 808 is inconsistent (some notes louder than others), the low band compression addresses this.
• Mid band: This is where the musical content lives. Compress gently to add density and cohesion. Over-compressing the mids makes the master sound flat and lifeless.
• High band: Hi-hats and cymbals can be spikey. The high band tames these peaks so the limiter does not clamp down on the entire mix every time a hi-hat hits.

Stereo Imaging and Width

Stereo imaging controls how wide or narrow the mix sounds. Proper stereo treatment ensures the mix sounds good on both stereo speakers and mono playback (phone speakers, Bluetooth speakers).

Using JSFX Stereo Width

Search for "stereo" in the FX browser and add a JSFX stereo width plugin. Key operations:

• Mono the bass: Apply a low-frequency mono filter that collapses everything below 100-150 Hz to mono. This prevents phase cancellation in the bass range, which causes low-end loss on mono playback systems. Many JSFX stereo plugins include this feature.
• Subtle widening: Increase the stereo width of the high-frequency content (above 5 kHz) by 10-20%. This adds openness and air without destabilizing the center image. Do not over-widen. Excessive width causes phase issues and sounds hollow on headphones.
• Mono check: Toggle the stereo plugin to mono output and listen. If the mix loses significant content or sounds noticeably different, you have phase issues that need addressing in the mix, not the master.

Limiting and Loudness with ReaLimit

ReaLimit is the final plugin in your mastering chain. It is a true peak brickwall limiter that prevents audio from exceeding a set ceiling while maximizing loudness.

Configuring ReaLimit

1. Insert ReaLimit as the last plugin on the Master track (before any metering plugins).
2. Set the Ceiling to -0.3 dBTP (true peak). This provides safety headroom for inter-sample peaks that can clip during digital-to-analog conversion. Never set the ceiling to 0 dB.
3. Gradually lower the Threshold to increase loudness. As you lower the threshold, the limiter engages more aggressively. Watch the gain reduction meter.
4. Target 3-6 dB of gain reduction for competitive loudness without audible distortion. Above 6 dB of gain reduction, you start hearing pumping and loss of dynamics.
5. Listen critically as you lower the threshold. When you hear the transients starting to lose punch, the dynamics starting to flatten, or the audio starting to distort, you have gone too far. Back off the threshold.

Loudness Targets

Metering and Loudness Standards

After ReaLimit in the chain, add a loudness meter to monitor your output. Search for "loudness" in the JSFX browser. Reaper includes a JS: Loudness Meter that displays integrated LUFS, short-term LUFS, momentary LUFS, and true peak values.

Reading the Meter

• Integrated LUFS: The average loudness over the entire track. This is the value streaming platforms use for normalization. Target -14 LUFS for streaming.
• Short-term LUFS: Average loudness over the last 3 seconds. Useful for checking if specific sections are significantly louder or quieter than the rest.
• Momentary LUFS: Near-instantaneous loudness. Shows peaks and transient levels in real time.
• True Peak (dBTP): The highest reconstructed peak value. Must stay below your limiter ceiling at all times. If true peaks exceed 0 dBTP, the audio will clip on playback.

Mastering for Different Formats

Streaming Master

Target -14 LUFS with ceiling at -1.0 dBTP. Export as WAV 16-bit, 44.1 kHz. This is what you upload to distributors (DistroKid, TuneCore, etc.) for Spotify, Apple Music, and other platforms. The platforms apply their own loudness normalization, so mastering louder than -14 LUFS just means the platform turns your track down, potentially making it sound worse than tracks mastered at the target.

Battle Master

Target -10 to -12 LUFS with ceiling at -0.3 dBTP. Export as WAV 16-bit, 44.1 kHz. Battle playback does not normalize loudness, so a louder master has more perceived impact. Push the limiter harder than you would for streaming, but stop before you hear distortion or pumping.

Rendering the Final Master

1. Set a time selection over your full track.
2. Go to File > Render or press Ctrl+Alt+R (Windows) / Cmd+Option+R (Mac).
3. Set format to WAV, 16-bit, 44.1 kHz for the final delivery master.
4. Enable Dither/Noise shaping if exporting to 16-bit from a 24-bit or higher session. Dithering adds a tiny amount of shaped noise that preserves audio quality during bit-depth reduction.
5. Name your file with a clear convention: "TrackName_Master_v1.wav"
6. Click Render.

Battle Mastering: Quick and Effective

When the battle clock is running, you do not have time for a full mastering session. Use this rapid mastering chain:

30-Second Master Chain

1. ReaEQ on Master: High-pass at 25 Hz. One move, 5 seconds.
2. ReaLimit on Master: Ceiling at -0.3 dBTP. Lower threshold until gain reduction shows 4-6 dB. Listen for distortion. If clean, move on. 15 seconds.
3. Level check: Play the loudest section. If the limiter is working too hard (pumping, loss of transients), back off the threshold. 10 seconds.

This three-step process takes 30 seconds and produces a master that is loud, clean, and ready for battle submission. It is not a perfect master, but it is a competitive one. Save the detailed mastering for release versions after the battle.

Frequently Asked Questions