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Use solo to find problems, not to set tone

A part you EQ in solo is heard in the mix through everything around it. Use solo for clicks, noise and rings, and make tone decisions with the mix playing.

· 6 min read Lesson 6 of 44 in Mixing & Mastering

In short

  1. Use solo for things that belong to one track alone: clicks, edits, noise, hum and rings, then unsolo before you decide anything about tone or level.
  2. In the mix a part is heard mostly through the bands nobody else covers, so a boost where the bass and keys already cover it feeds the low-mid build-up and adds little you can hear as the part.
  3. Check what your DAW does to effect returns in solo, or mark them solo safe, so a soloed vocal is judged with its reverb.
In this lesson (8)
  1. The guitar that sounded great alone
  2. The listener hears the sum
  3. Masking decides which part of a sound you hear
  4. Two EQs, one guitar
  5. Making every part complete
  6. Solo to find, unsolo to decide
  7. Check yourself
  8. Sources

The guitar that sounded great alone

You spend ten minutes on the acoustic guitar with solo on. A low shelf for body, a little air on top, and it sounds like an album intro. Then you unsolo. The guitar is no clearer than before, the bass has lost its edge, and the low end of the vocal is blurred. The body you added went straight into the range the bass and the piano were already filling. Solo showed you a guitar nobody will ever hear on its own.

Why it matters

The listener hears the sum

A listener never presses your solo button. They hear every part through every other part, so a part's tone in the mix depends on what plays alongside it. A guitar can be full and warm in solo and thin in the mix, or thin in solo and exactly right in the mix.

Solo is still the right tool for anything that belongs to one track alone: a click at an edit, a breath cut off mid-word, hiss, hum, a ring that keeps sounding after the note (see how to hunt a ring). It is the wrong place to decide tone and level, because those depend on everything else.

The science

Masking decides which part of a sound you hear

Inside the ear, sound is analysed in narrow overlapping bands. Within a band, a louder sound raises the level a quieter one needs to be heard at all (Fastl and Zwicker, 2007). The lesson on mud works through the band widths. What matters here is the consequence: in a full mix, a part is heard mostly through the bands where it is not covered.

Figure 1. Shapes, not measurements. Soloed, the whole guitar is audible. In the mix its lower part sits under the bass and keys, so what the listener hears as guitar is mostly the range above them, where nothing else is as strong.

Even where a part stays audible, it sounds weaker than in solo. Moore, Glasberg and Baer (1997) modelled this partial loudness, the loudness of a sound in the presence of another, and it is lower than the same sound's loudness alone. So in solo you judge the whole spectrum at full loudness. In the mix you hear a slice of it, turned down.

This explains the guitar. Its low mids sit under the bass and keys, so the shelf added energy the listener cannot pick out as guitar. That energy still counts, though: it raises the on the bass and on the lower part of the vocal. The guitar's identity in the mix lives higher up, in the pick attack and string detail, the part a soloed guitar can make sound too sharp.

It works the other way too. Some problems only exist together. Two parts that each sound clean can pile up in one range, and a bright part can sit right on top of the vocal's consonants. Neither shows up in solo.

The demo puts a bright pad in the same range as a lead. Cut the pad or duck it and the lead comes forward without getting louder, which is the same effect from the other side: how clear a part sounds depends on what plays around it.

Listen

Free a lead from a crowded pad

A lead and a bright pad share the same range. Cut the pad or duck it under the lead and the lead comes forward without getting louder.

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Start with your speakers or headphones low.

Solo has one more trap that has nothing to do with hearing. Depending on the DAW and its settings, soloing a track can mute the reverb and delay returns it feeds. A vocal judged that way sounds drier and harder than it is, and the reverb or brightness you add to compensate is too much once the returns come back.

Try it

Two EQs, one guitar

0 of 6 steps done

Version B often sounds smaller alone and works better in the mix. Version A often sounds better alone and leaves the vocal and bass less clear.

Common mistake

Making every part complete

You try to make each part sound finished on its own. Supporting parts are allowed to sound plain in solo, as the lesson on EQ as attention design argues. If every part gets body and air in solo, they all compete for the same bands and the mix turns thick and harsh at once.

Figure 2. Two EQs for one acoustic guitar, drawn from the filter maths. The solo EQ adds a 4 dB low shelf for body and 3 dB of air. The mix EQ takes 4 dB out of the same low range, where the bass and keys already cover the guitar, and lifts 2 dB around 3 kHz, where the guitar is still heard.

The opposite mistake is never soloing. Clicks, noise and bad edits hide under a full mix and then show up on headphones or in a quiet intro. Solo for those, fix them, and get out.

Takeaway

Solo to find, unsolo to decide

Make the habit concrete: any move made in solo gets checked in the mix before you keep it. When two parts fight, solo just those two, such as the kick and the bass or the vocal and the guitar, then bring the rest back before you commit. Spend most of the session with everything playing, because that is the only version anyone else will hear.

3 questions

Check yourself

  1. Which of these is a good job for the solo button?
  2. A low shelf on the acoustic guitar sounded fuller in solo. Why does it often add nothing to the guitar in the mix?
  3. You solo the lead vocal, find it dry and add more reverb. With the mix back it sounds far too wet. What is the likely cause?

Sources

Show all 2
  • Fastl, H., & Zwicker, E. (2007). Psychoacoustics: Facts and Models (3rd ed.). Springer.
  • Moore, B. C. J., Glasberg, B. R., & Baer, T. (1997). A model for the prediction of thresholds, loudness, and partial loudness. Journal of the Audio Engineering Society, 45(4), 224-240.

Next lesson · 7 of 44

Hard panning does not cure maskingPanning changes where a part comes from, not which bands it fills or when it plays. The help shrinks on speakers and disappears in mono, where the parts collide again.

Previous: Turning up a buried vocal rarely fixes it

Portrait of Virzy Guns

Written by Virzy Guns

Songwriter and producer, founder of Virzy Guns Production. Now building HealingWave.

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Later in Mixing & Mastering

See all 44 lessons

  1. EQ is attention designBoost the presence range on every track and nothing stands out. Use EQ to build contrast, so the part that matters is the one the ear can follow.
  2. Set each high-pass from the lowest noteA high-pass on every track removes notes as well as rumble. Work out each part's lowest note, filter only what sits below it, and only when it causes a problem.
  3. Depth needs contrast to existReverb on everything flattens a mix. Depth comes from contrast: a dry, bright, close part next to quieter, darker and wetter parts further back.