File Prep for Mixing & Mastering - A Practical Guide for Artists and Producers.

If you've ever sent files to a mixing or mastering engineer and got a message back asking for everything again — formatted differently — you'll understand why file prep for mixing & mastering matters. It costs everyone time, delays the project, and honestly, it's just a bit embarrassing when it happens repeatedly. And trust me, I have had returning clients make the same mistakes again and again.

Whether you're a metal band recording in your rehearsal space, a home-studio producer putting together a heavy music record, or someone with a proper studio setup, this guide walks you through exactly how to prepare your audio files for professional mixing and mastering. Get this right, and your engineer can focus on making your music sound incredible — which is the whole point.

Why File Prep Actually Matters

Mixing and mastering engineers aren't filing clerks. When you send over a disorganised mess of files — wrong formats, mismatched lengths, unlabelled tracks, no tempo info — the first thing that happens is an admin session that eats into the creative work. That's your money and your time going into problem-solving before a single fader has been touched.

Beyond logistics, poorly prepared files can actively hurt your music. If your guitars were clipping on the way in, no amount of clever processing can undo that distortion. If your tracks don't all start from bar 1, the engineer is playing a guessing game with alignment. If you've baked a limiter into your tracks, you've already made a decision that should have been left to the mixing/mastering engineer.

Clean, organised, properly prepared files give your engineer a clean canvas. They arrive ready to work, not ready to fix your admin.

Part One: Recording Standards

Before we even get to the export stage, let's talk about how the audio should be captured in the first place. This is especially important for heavy music, where the recording quality — and in particular, guitar, bass, and vocal recordings — can make or break a mix.

Audio Format

For all audio files, the standard you should be working to is WAV, 24-bit, at either 44.1 kHz or 48 kHz. That's it. Not MP3. Not AAC. Not a voice memo from your phone. WAV files are uncompressed and give your engineer the full resolution they need to work with.

If your DAW session is set to 44.1 kHz, export at 44.1 kHz. If it's at 48 kHz, export at 48 kHz. Don't change the sample rate at the export stage — let the mastering engineer handle any conversion with mastering-grade tools.

Guitars and Bass: Record DI

For rock, metal, and any kind of heavy music — record a clean DI track. Always.

A DI (direct input) is a clean, unprocessed signal recorded straight from your guitar or bass into your interface, before any amp simulation or processing is applied. It is the foundation of your metal tone and is non-negotiable in professional heavy music production.

Here's why DI matters:

●      If the amp simulation or cab tone isn't working in the mix, your engineer can reamp the DI through a real amp or try different amp sims — without you having to re-record anything.

●      A clean DI waveform makes editing dramatically easier. You can actually see the pick attack transients, which is essential for tightening up rhythm parts. Some engineers won't accept a project without them.

●      It gives your mixing engineer flexibility. That's the whole idea.

What to watch out for when recording DI:

●      Do not clip. Set your input level so that peaks during the most aggressive parts land somewhere between -12 dBFS and -10 dBFS on your interface's input meter. A clipped DI is completely unusable. (unless it is a creative decision...which is debatable).

●      Do not process the DI on the way in. No EQ, no compression, no noise gate at the recording stage. Keep it raw. Any processing you bake in is permanent.

●      Use decent cables. A noisy cable adds noise to every single take. Invest in reliable cables — Mogami are a solid choice.

●      Check your guitar setup. Pay attention to string noise, fret buzz, and any other unwanted noise that would be difficult to remove later.

Most Importantly, USE NEW STRINGS! For heavy music specifically: if at all possible, use a fresh set of strings for every song (same gauge and brand throughout). Fresh strings give you better transient definition, more articulation on fast picking, and a sharper, tighter attack — all of which come through in a mix in ways that genuinely matter.

Vocals

Vocal recording quality will always affect the final result. Ideally, you want to record in a professional studio with a quality microphone preamp. For rock and metal vocals especially, a preamp with some character — some colour — works well. If the studio has an outboard compressor available, use it: for heavy genres, you can typically aim for around 6–10 dB of gain reduction during the heaviest, most dynamic passages.

If you're recording at home and your options are more limited, don't worry — just get in touch with us before the session and we can work through the setup together.

Regardless of where you record:

●      Control the room. Manage background noise, room reflections, and floor noise as best you can.

●      Watch your levels. Vocal peaks should ideally stay below -6 dBFS. Clipped vocals are not something anyone can undo.

●      Edit your vocals before sending. Clean up breaths, excessive room noise between phrases, clicks and pops, and any takes you don't want included.

●      If the vocals need pitch correction, get that done before you send the files — or at minimum flag it up so the engineer knows what's needed.

Part Two: MIDI Drums

If you're using a drum plugin — Superior Drummer, Addictive Drums, EZdrummer, or similar — rather than recording a live kit, you have two options: send the MIDI file itself, or export the individual drum channels as audio.

If sending the MIDI file directly, please add a kick drum note (C1) on beat 1 of bar 1 as a reference point. This is used to confirm proper alignment once the MIDI is imported into the mixing session. It will be removed during the session, but it's essential for making sure everything lines up correctly.

Kick Drum Note (C1) on Beat 1 of Bar 1

If exporting drum audio from MIDI, export each drum element — kick, snare, hi-hats, toms, overheads, room mics — as separate audio files, just as you would with a real recorded kit. This gives the engineer full control over the drum sound in the mix.

Why not just leave it in MIDI? Bouncing MIDI drums to audio means you get consistent, repeatable results every single time. Plugins that use round-robins and humanisation can produce slightly different results on each playback, which can cause alignment issues. Audio is locked in. As a general rule — all non-drum MIDI instruments (orchestration, synths, additional melodic or harmonic layers) should also be bounced to audio before sending.

But for the best results possible, send both the Drum MIDI file and the bounced audio, so we can determine what is the best way to approach the drums.

Part Three: Export and Alignment

This is where a lot of projects fall apart. The recording quality can be excellent, but if the files aren't exported correctly, everything grinds to a halt on the engineer's end.

Start Everything from Bar 1

Every single audio file must be exported starting from bar 1, beat 1 of your project, regardless of when the actual audio content begins. If your lead vocal doesn't come in until bar 9, the file still starts from bar 1 — with empty silence filling bars 1 through 8. This ensures that when the engineer imports all your files into their session, everything lines up perfectly with zero manual alignment required.

Think of it this way: every file should open up in the DAW looking like a complete, full-length track — just with silence where there's no audio content.

Make Every File the Same Length

All exported files must be exactly the same length. If your longest track runs to 3 minutes 47 seconds, every other file in that delivery should be exactly 3 minutes 47 seconds, even if a particular instrument only plays for the first two minutes. Pad the shorter files with silence.

This makes the engineer's import workflow clean and fast. They shouldn't be measuring and dragging files into position.

An Example of How The Files Should Look Like After We Imported Them

Include a Tempo Document

For every song, provide a written document that lists:

●      The BPM of the song

●      Any tempo changes — when they occur (measured from bar 1, beat 1), what bar they happen on, and what tempo they change to

●      Any time signature changes, noting the same information

If your song runs at a constant 170 BPM throughout, this is simple. If you've got a track that drops from 180 to 92 and back again halfway through, document it precisely. This information is essential for the engineer to set up their session correctly.

Part Four: Headroom and Levels

For Mixing

If you're sending individual tracks for mixing, the general principle is simple: don't clip, and leave some room. Your individual tracks should not be slamming 0 dBFS. Peaks sitting around -12 to -6 dBFS on a typical session are generally fine. The exact numbers matter less than the principle: give the engineer space to work.

For Mastering

If you're sending a stereo mix file for mastering, aim for peaks around -6 dBFS with an average (RMS/LUFS) somewhere between -18 and -12 dBFS. This gives the mastering engineer enough headroom to apply their processing without immediately running into the ceiling.

Critically — remove any limiting from your master bus before exporting your mix for mastering. Compression and limiting cannot be undone. If you want to send a version with your master bus processing for reference, go ahead — but also send a clean, limiter-off version. That's the version the mastering engineer actually works from.

Do not apply dithering, do not normalise the file before export. Export at 24-bit (or 32-bit float) at your session's native sample rate.

Part Five: Clean-Up

Nobody wants to work on a project where the audio files are full of noise, pops, and clicks that could have been cleaned up beforehand. Go through your material carefully — with headphones — and sort out the following before you send anything:

●      Clicks and pops. Check every edit point and crossfade. These can be hard to spot when you're deep in a session, but they jump out immediately in a finished mix.

●      Noise between phrases. Especially on vocal tracks — clean up the sections between lines. Room noise, handling noise, breath noise in the wrong places: sort it.

●      Silence at the start. Check the very beginning of each file for any stray noise before the music begins.

●      The tail. Check the end of the song for any unwanted sounds after the music fades out. Leave a few seconds of natural room tone or silence — don't hard-cut right at the last note.

And critically — listen back to your exported files. This sounds obvious, but DAW glitches and plugin rendering errors happen. Always listen to the actual bounced file before you send it.

Part Six: File Naming and Organisation

Label your files in a way that makes sense to someone who wasn't in the room when you made the session. Common categories for heavy music:

●      Drums: `Kick_In`, `Kick_Out`, `Snare_Top`, `Snare_Bottom`, `HiHat`, `Toms_L`, `Toms_R`, `Overheads_L`, `Overheads_R`, `Room`

●      Guitars: `Guitar_L`, `Guitar_R`, `Guitar_DI_L`, `Guitar_DI_R`

●      Bass: `Bass_DI`, `Bass_Amp`

●      Vocals: `Lead_Vox`, `Backing_Vox_L`, `Backing_Vox_R`

●      Other: `Strings`, `Orchestral_Bus`, `Synth_Layer`

Number-code the tracks, so they can be imported in a logical sequence. At NK Audio, we like to work with the order: Drums, Bass, Guitars, Additional Guitars, Keys, Effects and Vocals. So your numerical sequence you follow that order. (01. Kick_In, 02.Kick_Out........20.Vocal). However, this might differ from project to project.

Put everything in a clearly named folder: Artist Name – Song Title – BPM. If you're delivering multiple songs, each song gets its own folder. Include the tempo document inside the relevant song folder.

For mastering specifically, name your stereo mix file clearly with the song title and version number — something like `SongName_Mix_v3.wav`. Avoid naming anything "FINAL" — it's bound to not be final, and you'll end up with files named `FINAL_actual_FINAL_v4.wav`.

Part Seven: What to Include When You Send

When you deliver your files, don't just drop a folder in a shared link and disappear. Include:

●      A rough mix for reference. This gives the engineer a quick impression of what you're going for — the balance, the vibe, the direction. Even a rough bounce from your session is more useful than nothing. It does not have to be flashy and don't be afraid to send a "bad" mix, this is just to show your mixing engineer what you vision roughly is. Besides, what do you want your mixing engineer or mastering engineer to do if you can make a world-class-sounding track yourself?

●      Reference tracks. Send a link or file for one or two commercially released songs that represent the sound you're aiming for. Not because the engineer is going to copy them, but because it communicates intent clearly and quickly — faster than any written description.

●      Notes. If there's anything specific you want the engineer to pay attention to — a particular section, an effect you want more or less of, a specific arrangement decision — write it down. The more clearly you communicate upfront, the fewer revision rounds you'll need.

For Mastering: If you have ISRC codes and metadata ready to go, include them too — especially if the project is heading to distribution. Artist name, album/EP title, track titles, and track sequence are the minimum.

Quick Reference Checklist

Before you send anything, run through this:

Recording

☐  WAV format, 24-bit, 44.1 kHz or 48 kHz

☐  DI tracks recorded for all guitars and bass (no clipping, unprocessed)

☐  Guitar peaks between -12 and -10 dBFS

☐  Vocal peaks below -6 dBFS

☐  Fresh strings used for guitar/bass recording

☐  Vocal editing done (breaths, noise, tuning if needed)

MIDI

☐  Drum MIDI: C1 kick note added on bar 1, beat 1

☐  All non-drum MIDI exported as audio

Export and Alignment

☐  All files start from bar 1, beat 1

☐  All files are the same length

☐  Tempo document included (with all BPM and time signature changes)

Levels and Processing (for mastering)

☐  Master bus limiter removed before export

☐  Mix peaks around -3 dBFS

☐  No dithering applied

☐  No normalisation applied

Clean-Up

☐  Clicks, pops, and stray noises removed

☐  Noise between vocal/instrument phrases cleaned up

☐  Exported file listened back in full before sending

Organisation and Communication

☐  Files clearly named

☐  Files organised in labelled folders

☐  Rough mix included

☐  Reference tracks included

☐  Notes and any special requests included

If you follow this guide, your mixing or mastering engineer will be able to load up your session and get straight to work. No back-and-forth, no unnecessary delays. Just the music.

If you have any questions about how to prepare your specific project for NK Audio's mixing or mastering services, feel free to get in touch.

Check out our recommendations for reliable recording interfaces and DI boxes for different budget ranges. (Affiliated Links):

Focusrite Scarlett 2i2: https://amzn.to/3NyGxbr

Audient ID24: https://amzn.to/4sh3lvn

RME Babyface: https://amzn.to/4lzGIQB

Radial Pro48 Active DI Box: https://amzn.to/4sjWnGg

Rupert Neve Design DI Box: https://amzn.to/4lLRpiX

References: Waves (waves.com/how-to-prepare-mix-for-mastering)  |  Pro Audio Files (theproaudiofiles.com/mastering-preparation)  |  Alexander Wright Mastering (alexanderwright.com/blog)  |  Sage Audio (sageaudio.com)  |  Nail The Mix (nailthemix.com/how-to-record-a-guitar-di)  |  Frightbox Recording Academy (frightboxrecordingacademy.com/clean-di-tracks)  |  Mastering.com (mastering.com/program-realistic-midi-drums)