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Stem mastering

Stem mastering, also known as stem mixing, is like using the sub groups on a live mixing console. Instead of everything being summed to the stereo master output to create a single stereo mix file, you can break the mix down into the specific parts. These parts can then each receive special attention in the mastering session.

For example, you could create a stereo drum track stem, a stem combining a stereo vocal track with backing vocals and vocal effects mixed in, and a final stem combining the remaining instruments. These stems are exported with the exact same start time, then assembled again in a multi-track stem mastering session where the mastering engineer can address these mix problems more effectively. For instance, we could EQ the bass guitar without altering other areas of the mix, de-ess the vocals without effecting the cymbals, raise or lower the drums for more or less impact.

Why do it?

Under the right circumstances, stem mastering can make a very big difference to the sound of the finished master. Stem mastering effectively finishes off the mix in a controlled environment, which in turn helps the mastering process achieve the maximum sonic potential for the project. Clients with limited mixing experience, engineers with poor monitoring, and recordings produced with low budget equipment can all benefit from stem mastering.

Does it cost more?

Stem mastering is more expensive than mastering a stereo track. Because the time may vary from project to project, stem mastering is based on an hourly rate. The time required largely depends on the quantity and quality of the stem files provided and how much work is required to obtain the best results.

Should I do stem mastering?

Why not discuss stem mastering with Matthew before your session to find out if it will benefit your next project.

How do I prepare for stem mastering?

Once you've decided that stem mastering is right for you, follow these steps to get the most out of the mastering process and avoid any unnecessary delays along the way.

1. Set the correct bit depth and sample rate

Export 24-bit integer or 32-bit floating WAV files at the project sample rate, as you would when delivering a stereo mix. Depending on how you gain stage, 32-bit floating may be the better option since it will ensure that clipping cannot occur.

2. Export all stems as stereo

This preserves the correct balances in the mix and maintains any stereo effects and panning.

3. Ensure all stems have the same starting point

This makes it easy to recreate the correct timing and structure of the original mix.

4. Don’t normalise the stems

Normalised stems results in a wildly-unbalanced mix when summed together.

5. Use descriptive filenames

Descriptive filenames help the mastering engineer to quickly and accurately locate the correct files. Here are examples of well-named files:

6. Check that the stems sum to match the full mix

Most importantly, once you’ve exported all stems, bring them back into your DAW and check that they add together to correctly recreate the mix. There are various reasons why they might not perfectly match; here are a couple of the more common reasons:

  • Duplicated effects, for example when vocals are sent pre-fader to a reverb. Depending on the DAW settings, that reverb might end up on both the vocal and the instrumental stem; double check that all effects are printed only once to the appropriate stem.
  • Non-linear processing on busses, for example compression on the mix bus. The stems will not perfectly match the full mix because the processing acts differently when printing separate stems; you might need to key the bus processing when exporting the stems by feeding the full mix to their external sidechain inputs so that they behave properly.

7. Include a full stereo mix when delivering the stems

Providing a reference mix enables the mastering engineer to do a quality check and confirm all elements of the mix are present in the final stem-mastered product.