How It Works
A notch filter — also called a band-reject or band-stop filter — is a specialized EQ that cuts a very narrow frequency band with extreme precision. While a standard parametric EQ cut might use a Q of 2-4, a notch filter uses a Q of 10, 20, or even higher, targeting a razor-thin slice of the spectrum. The cut depth can be severe (10-30 dB or more) without audibly affecting the frequencies on either side.
The most common use case is removing tonal problems that exist at a single specific frequency: mains hum at 50 Hz or 60 Hz (depending on your country's electrical system), monitor feedback at a specific resonant frequency, a snare drum ring at its fundamental pitch, or a room resonance that booms on one particular note. Because the notch is so narrow, removing the offending frequency does not change the overall tonal character of the sound.
Notch filters are also available as dedicated plugins (often called "surgical EQ" or "precision EQ" tools) and as a specific filter type within parametric EQs. Some plugins offer automatic resonance detection that identifies problematic frequencies and suggests notch positions, speeding up the process of finding and eliminating specific tonal issues.
Why It Matters for Your Mix
Some frequency problems are so specific and narrow that a standard EQ cut would affect too much of the surrounding spectrum. A snare drum with an annoying ring at 680 Hz needs surgical attention — a broad EQ cut centered at 680 Hz would remove body and character from the snare, while a narrow notch cut targets only the ring. Similarly, removing 60 Hz mains hum requires a notch so narrow that the bass frequencies around it are preserved. Notch filters are the scalpel of the EQ world. Where a parametric EQ is a general-purpose tool for broad tonal shaping, a notch filter excels at removing single-frequency problems with minimal collateral damage. It is an essential technique for cleaning up problematic recordings and taming resonant behavior in rooms and instruments.
Common Mistakes
Using notch filters for broad tonal adjustments
A notch filter is not the right tool for general EQ shaping. If you need to reduce muddiness in the 200-500 Hz range, use a standard parametric cut with a moderate Q. Notch filters should be reserved for single-frequency problems like hum, ring, and feedback.
Stacking too many notch filters
If you find yourself needing five or more notch filters on a single track, the problem is likely in the recording or the room, not something that can be EQ-fixed. Consider re-recording, using noise reduction software, or addressing the acoustic environment.
Not verifying the exact problem frequency
A notch filter that is off by even 20-30 Hz will miss the target entirely while cutting a perfectly good frequency. Use a spectrum analyzer, a frequency sweep, or your plugin's frequency identification feature to pinpoint the exact problem frequency before placing the notch.
What RoastYourMix Measures
RoastYourMix does not detect single-frequency peaks such as hum or ringing, because it measures four broad bands rather than a high-resolution spectrum. Finding a frequency to notch is a job for a spectrum analyzer and a narrow EQ sweep.
See Notch Filter in Action
Upload your mix and see its loudness, true peak, tonal balance and stereo width measured.
The quick answers
How do I find the exact frequency to notch?
Set a parametric EQ band to a narrow Q with a significant boost (+8 to +12 dB) and slowly sweep it across the frequency range. When the problem frequency is amplified, it will become very obvious — the hum, ring, or resonance will jump out. Note that frequency, remove the boost, and apply a narrow cut at that exact point.
Can a notch filter remove 60 Hz hum completely?
A notch at 60 Hz will remove the fundamental, but mains hum also produces harmonics at 120 Hz, 180 Hz, 240 Hz, and so on. To fully remove hum, you may need notch filters at multiple harmonic frequencies. Some specialized hum removal plugins handle this automatically.
What is the difference between a notch filter and a dynamic EQ cut?
A notch filter is always active — it permanently removes a specific frequency. A dynamic EQ cut only engages when the problematic frequency exceeds a threshold. If the resonance is constant (like hum), use a notch. If it is intermittent (like a drum ring that only happens on certain hits), a dynamic EQ is more transparent because it only cuts when needed.