Low end

Your bass shakes the room on your monitors. On your phone, it's gone: the kick taps away, the vocal is fine, and the bass line has simply left the song.

The lab below starts on Small speaker, a rough stand-in for a phone or laptop: everything below 180 Hz is filtered out. Listen to the bass line. Can you still tell which notes it's playing?

To bring the line back on a small speaker, should you add more deep bass, or something else?

With Presence at zero, the notes are vague, a muffled thump at best. Raise it and the line comes back: you can follow every note again, even though the speaker still can't play the deep part. Switch Listen to Full and you'll find the room-shaking weight is still there, barely changed.

If you guessed "more deep bass", that's the instinct almost everyone starts with. But a small speaker can't play those frequencies however much you feed it. More sub just hits the same wall harder, and steals headroom from everything else.

Weight and notes are two different jobs

A bass part does two things at once:

• Weight: the deep fundamental you feel in your chest. On a big system, it's what makes the drop land.
• Notes: the clues that tell you what it's playing. These live mostly in the harmonics above the fundamental.

You met this in Timbre and harmonics: take away a note's fundamental and your ear still hears the pitch, as long as enough of the harmonic ladder remains. That's what Presence does here. It adds a layer of gentle distortion to the bass, which creates new harmonics higher up, where small speakers can play them. Your ear reads their spacing and fills in the missing note.

This is why so many trap and hip-hop producers push their 808s through saturation. A pure 808 sine is huge on a club system and close to invisible on earbuds. A bit of grit gives it harmonics that survive almost anywhere.

Match the level, then judge

Adding harmonics makes the bass louder, and louder always sounds better (see Listening and comparing). So before you decide, toggle the effect to Bypass and use Match level to even out the loudness. Now ask the honest question: at the same level, can you follow the notes more easily?

Adjust level with the final output, not by turning Presence down, or you'll change the very thing you're testing. And keep an eye on peaks: a lot of Drive and Presence on a hot bass can push past full scale.

Use Harmonics in the Listen menu to hear only the added layer. It should sound like a thin, buzzy ghost of the bass. If it sounds like a separate, nasty instrument, you've probably gone too far.

Always switch Listen back to Full before you judge the bass in your mix. Small speaker and Harmonics are for listening, not the sound you want to keep.

Not every bass needs this

A saw bass, a picked electric bass or an already distorted synth bass has plenty of harmonics of its own. Switch the lab's source to the bass guitar and compare: it may survive the small speaker better than the synth phrase with no help at all. Adding more grit to a bass that already translates can make it fizzy and crowded, and start competing with the guitars or the vocal.

Let the bass tell you what's missing. If you can follow the line on a small speaker, leave it alone.

Kick and bass: who goes first?

Harmonics fix translation. They don't fix collision. If the kick and bass both start a long, low boom at the same instant, they'll blur together however clear each one is alone.

Give each a job in time:

• Short kick, long bass: the kick is a punch that marks the beat, then gets out of the way so the bass can sustain. Common in funk, disco and house.
• Long kick, short bass: a long, booming kick (like an 808 kick) carries the low end, and the bass plays short notes in the gaps, or higher up.

Tails matter as much as attacks. Shorten the kick's decay a little, or the bass note's release, and listen to the groove open up.

Many producers also tune the kick to the song's key, or to a note that sits well with the bass line, so a long kick tail doesn't clash with the bass notes it overlaps. It's worth trying, not a rule.

Ducking the bass under the kick

Sidechain compression turns the bass down for a split second every time the kick hits, then lets it back up. It's how a lot of dance music keeps a huge kick and a huge bass from fighting. It needs a compressor that can listen to the kick while processing the bass, so check that yours has a sidechain input. Gates, sidechain and ducking shows how it works.

Phase: when low notes cancel

Two low sounds playing at once can partly cancel each other if their waves are out of step: one pushing while the other pulls. A kick and bass that sound fat alone can sound strangely thin together. Flipping the polarity of one of them, or nudging its timing by a few milliseconds, can bring the weight back.

The catch: a moving bass line has a different relationship with the kick on every note. Fix the first hit and the fourth one might get worse. Listen to the whole phrase, not just the downbeat.

And check in mono. Keep the core of the low end in the centre, where it's strongest on every system. Wide, stereo bass textures are fine on top, but the foundation shouldn't depend on them.

Where it breaks

• Too much harmonic layer makes the bass gritty and starts fighting the kick's click and the low mids.
• Very high Drive can raise the deep fundamental too, not just the harmonics, so the weight creeps up along with the clarity.
• No small-speaker test is a real phone. The Small speaker setting is a useful filter, not a model of any particular device. Always do one last check on an actual phone or laptop, at a normal volume.

Same idea, different place: church organ builders used the same trick centuries before phones. Timbre and harmonics explains how two higher pipes can make your ear hear a pitch that no pipe is playing.

Make it yours

Pick a song of yours with a bass line that disappears on small speakers. First, check it really needs help: play it on your phone and see whether you can hum the line.

If you can't, open Bass Presence Lab on the bass, start on Small speaker, and raise Presence until you can just follow the notes, then a touch more. Match the level against bypass. Switch back to Full and check the weight hasn't ballooned.

Then bring in the kick. Decide whose job the low boom is, and shorten the other one's tail. Listen on your monitors, your phone and in mono.

Save the preset with a role note in the name, like "Bass: notes on small speakers, kick owns the boom". It tells future you both halves of the decision.

Quick check

1. Your bass disappears on a laptop, so you boost 50 Hz by 6 dB. On the laptop, nothing changes. On your monitors, it's now boomy and the master is clipping. What went wrong? The laptop can't play 50 Hz, so the boost only landed on systems that could already play it, and used up headroom. Add upper harmonics or choose a brighter bass sound instead.
2. After adding harmonics, you can follow the bass on your phone, but the kick and bass still sound like one blurry thump on the downbeat. Will more Presence fix it? No. That's a timing and tail problem, not a translation problem. Shorten one of the tails, give each a different job, or duck the bass when the kick hits.
3. Your bass sounds thin only when the kick plays, though both are fat alone. What could cause that? Phase cancellation between their low frequencies. Try flipping the polarity of one or nudging its timing, and check the whole phrase, not just one hit.

Next steps

• Go deeper: Depth and space in a mix. The low end is solid and centred. But now every part sits in the front row. How do you push something back?
• Sideways: Drum synthesis. Shape the kick's body and tail at the source instead of fixing them later.