Q is the setting that describes how narrow or wide a range of frequencies an EQ or filter acts on. It is related to bandwidth. In general, a higher Q means a narrower affected range and a lower Q a wider one. A notch aimed at a specific resonance uses a higher Q, while gentle overall tone shaping uses a lower one.
How Q and bandwidth relate
Bandwidth is how far the effect reaches out from the center frequency. Q is the measure of that narrowness: at the same center frequency, the higher the Q, the narrower the bandwidth. Since the display and the feel of the numbers differ between DAWs, check with both the graph and your ears.
When a wide Q suits
For gently adjusting low-end weight, slowly changing overall brightness, or naturally shaping a vocal’s presence, apply a gentle change across a wide range. Wide moves are less likely to sound unnatural, but they also affect other instruments more easily, so check them in the full mix.
When a narrow Q suits
A narrow Q is a candidate when you are taming a problem with a fairly definite location, such as a resonance, a piercing component, or hum. Temporarily boost a narrow band to find the spot, then cut it by the smallest amount once you have. It is important not to leave the extreme search setting as your final one.
Relationship to filter shape
On peaking EQs, notches, and band-pass filters, Q sets the width around the center frequency. On high-pass and low-pass filters, Q or resonance may instead affect emphasis around the cutoff. The same Q value sounds different depending on the filter type, so do not judge by the number alone.
How to compare settings
When you change Q, match the output level and compare on versus off and wide versus narrow. If it sounds good soloed but unnatural in the song, put it back. The basics of EQ, including Q, are covered in the EQ article.
