Mastering delivery formats: what to deliver

Agree the required formats with the client or distributor, then label the delivery files clearly. Keep reference copies separate from release masters.

The core deliverable: a high-resolution WAV

A stereo 24-bit WAV at the session sample rate is a common main deliverable. Check whether the distributor or recipient requires a different format.

• 24-bit, not 16-bit. Use 24-bit for the main delivery unless the recipient specifies otherwise. Create a separate 16-bit version when CD delivery is required.
• The session's sample rate, not a "better" one. Deliver a 44.1 kHz mix at 44.1 kHz, a 48 kHz mix at 48 kHz. Upsampling alone does not restore information absent from the source.

Most specs put the true peak ceiling at −1 dBTP (Amazon asks for −2), because lossy encoding on playback pushes inter-sample peaks higher. A peak reading alone does not tell you whether distortion is audible or intended. Check the recipient’s requirements and compare a decoded test encode with the source. If you want to see where a master sits, the free loudness meter reads true peak with oversampling, and this guide explains the difference between sample peak and true peak.

One master for streaming, a separate one for CD

You often deliver more than one file, but rarely for loudness reasons. Streaming platforms normalize playback, but delivery requirements still depend on the recipient. Confirm whether separate masters are needed. What genuinely differs is the destination format:

• Streaming and downloads. The 24-bit WAV at the session rate. This is what distributors ingest.
• CD. A 16-bit 44.1 kHz version, with a sample-rate conversion if the master was higher, and dither applied once at the bit-depth reduction. For replication, that usually means a DDP image rather than loose WAVs.

Choose the mastering level for the material and the brief. A platform’s normalization level is a playback reference rather than a requirement to master every track at that level.

DDP for physical: the disc standard

If the release is going to physical CD, the plant wants a DDP (Disc Description Protocol) image, not a folder of WAVs. A DDP is a single verified package that carries the audio, the track order and gaps, the PQ codes, and the embedded ISRCs, all in the exact layout the disc will have. It removes ambiguity from replication, which is why it's the standard. For streaming and downloads you do not need one.

Metadata and ISRC codes

The audio is only part of the handoff. Each track needs its ISRC code (the unique recording identifier), plus titles and album information, embedded where the format allows: in the DDP for disc, and provided alongside the WAVs for the distributor to attach. ISRCs come from the label or the distributor, not from the mastering engineer, so confirm you have them before the final render rather than after.

References, instrumentals, and the extras

Include an MP3 reference if the client wants a smaller file for casual listening. Label it clearly. Agree any instrumentals, clean versions, TV mixes or stems before preparing them.

Naming, headroom, and a quick checklist

Clear naming saves a round-trip. A convention like ArtistTitle_Master_24-48.wav tells the client what each file is at a glance. Before you send, run the list:

• 24-bit WAV at the session sample rate, true peak checked against the ceiling.
• A 16-bit 44.1 kHz version or a DDP image if there's a CD, dithered once.
• ISRC codes and titles confirmed and embedded where they belong.
• A labeled MP3 reference, and any contracted instrumentals or stems.
• Filenames that say what each file is, with no version ambiguity.

Check the delivery files and access settings

Keep the approved master, format variants and agreed extras together. Check access settings before sending the link. A checksum lets the recipient verify a downloaded file against the original.

Frequently asked questions

What does a mastering engineer deliver?

At minimum, a high-resolution stereo master as a 24-bit WAV at the session's sample rate, with true peak read against the ceiling for streaming. Depending on the release, that's joined by a 16-bit 44.1 kHz version or a DDP image for CD, a date-stamped MP3 reference for casual listening, and any contracted extras like instrumentals or stems. The metadata (track titles, ISRC codes) is embedded where the format allows.

What sample rate and bit depth should a master be delivered in?

Deliver the main master as a 24-bit WAV at the sample rate the mix was made at, commonly 44.1 kHz for music or 48 kHz for anything going to video. Upsampling alone does not add source detail. For CD, convert to 16-bit 44.1 kHz with dither applied once, at that final bit-depth reduction.

What is a DDP file, and do I need one?

A DDP (Disc Description Protocol) image is the standard master format for CD replication: it carries the audio, track order and gaps, PQ codes, and embedded ISRCs as one verified package. You need one if the release is going to physical CD; for streaming and downloads, high-resolution WAVs are what distributors want, not a DDP.

Do I need a separate master for streaming and CD?

Often yes, but not for loudness reasons. Streaming platforms normalize playback, and a single streaming master may be suitable. CD requires a separate format because CD is a 16-bit 44.1 kHz format, usually a DDP image with PQ codes and ISRCs. Read true peak against the ceiling either way (around −1 dBTP, −2 for Amazon), and treat loudness as a creative call for the song rather than a target to chase.

What file format should I send a mastered track in?

For the release master, send an uncompressed WAV (24-bit), not an MP3. An MP3 is fine as a labeled reference for quick listening, but it isn't the deliverable, because the client would be approving and releasing something lossy. Keep the WAV at the session's sample rate and deliver it in a way that preserves the exact file.