Finagle My Song · Blog
Why your bassline disappears on a phone speaker
You've had this happen. The track sounds massive on your monitors — bass fills the room, low end wraps around you. Then you check it on a phone speaker, a laptop, one earbud, a Bluetooth speaker in the kitchen. The bass is gone. Not quieter. Gone.
Most speakers you don't control are mono
Headphones and studio monitors give you two channels. A huge amount of the real world doesn't: phone speakers, laptop speakers, cheap Bluetooth speakers, one AirPod, a club system with a blown side, a voice assistant playing your song in someone's kitchen. All of these sum left and right down to a single channel before the sound leaves the box.
That summing is the moment your mix meets physics. If your left and right channels agree with each other, they add up and the sound holds together. If they don't agree, they start cancelling each other out — and the more they disagree, the more of your track quietly vanishes the instant it goes mono.
What "disagree" actually means
Every sample in your left channel has a matching sample in your right channel at the same moment. Correlation measures how well those two match, on a scale that runs from +1 to -1.
+1 means both channels are identical, sample for sample — completely mono-safe, even if the source is technically stereo. 0 means the channels are unrelated to each other, wide but risky. Negative numbers mean the channels are pushing in opposite directions: one speaker cone moving forward while the other moves back, the same instant. Sum that to mono and the two waves cancel. Literally silence, for whatever part of the mix that's happening to.
Our analyzer measures this directly on every upload as stereo correlation, and it's blunt about the bands: below 0.25, the mix gets flagged as a mono-compatibility warning. Below 0, it's flagged critical — actual phase cancellation, not just wideness.
Why bass takes the hit hardest
Any part of a mix can have correlation problems, but low end is where it costs you the most. Bass carries the bulk of a track's energy. Lose it and the track doesn't just get thinner — it loses its floor. A vocal or a hi-hat that partially cancels in mono is a small loss. A sub that cancels is the difference between a track that hits and one that doesn't exist below 200Hz.
The usual causes all feel like "making it bigger" while you're mixing on full stereo monitors: stereo widening plugins run across the whole mix instead of just the top end, doubled bass or synth parts panned hard and processed differently per side, wide stereo reverb or chorus left on a bass or sub layer, mid-side EQ pushed too hard on low frequencies. All of it sounds enormous in the room. None of it survives being folded down to one speaker.
The fix is narrower than it sounds
You don't need to flatten your whole mix to mono. You need your low end to be mono, or close to it, and everything above that can be as wide as you want.
Bass and sub — roughly anything below 150–200Hz — should sit at or near correlation +1. Above that, width is a creative choice, not a liability, because higher frequencies are shorter wavelengths and don't cancel the same way over the same physical distance. A lot of mixing chains handle this automatically with a mono-below-X filter on the master bus. If yours doesn't, it's worth adding one.
Check it, don't guess it
The honest problem is that your monitors are stereo, so you will never hear this on the system you mixed on. The only way to know for sure is to check it directly: hit the mono button on your interface or DAW master bus and listen for anything that thins out or vanishes, or look at an actual correlation number instead of trusting your ears on a system built to hide the problem.
That's what the stereo-correlation reading in Finagle My Song's free analysis is for — upload a track and it tells you straight away whether your low end will survive being summed to mono, before a listener on a phone speaker finds out for you.