Keep Your Low End Mono Below 100Hz — Here’s Why

Here’s a mixing rule that sounds boring until the moment you understand why it exists.

Keep your bass mono below 100Hz.

Not because some tutorial told you to. Because of physics.

Why low frequencies are mono by nature

Human ears cannot determine the direction of very low-frequency sounds. Below roughly 80–100Hz, the wavelengths are so long that your brain loses the ability to localize where the sound is coming from. Bass doesn’t come from the left or the right — it comes from everywhere.

This has a practical consequence: stereo bass information at very low frequencies doesn’t add width to your mix. It adds phase complexity. And phase complexity below 100Hz is almost always a problem.

What happens to stereo bass in mono

When a stereo mix is summed to mono — which happens on phones, most Bluetooth speakers, TV broadcasts, and club PA systems at distance — the left and right channels are added together. If the left and right low-end signals are slightly out of phase with each other, they partially cancel when summed. Your bass gets quieter. Possibly much quieter.

This is the most common reason for bass that sounds great in stereo and disappears in mono. Phase cancellation in the low frequencies.

The fix

Most DAWs have a way to apply different processing to different frequency ranges. Apply a stereo-to-mono effect on frequencies below 100Hz, or use a crossover-based plugin that keeps the lows in mono and allows the mids and highs to remain wide.

Alternatively, check your arrangement. If your bass instrument is a single mono channel — which it usually should be — there may be stereo reverb or delay on it creating width in the low end. Remove those effects from the bass, or high-pass filter the reverb return so it only carries mid and high-frequency content.

Check your mix in mono. If the bass loses more than 2–3dB when you hit the mono button, there’s a phase problem that needs attention.

Jacob Korn at tailout.de uses Mid/Side EQ at mastering to clean up low-end phase issues — but the most reliable fix is always catching it in the mix, where the source tracks are still accessible.

Ready to send your mix? Visit tailout.de — professional mastering that checks your low end translates everywhere, every time.