Q Factor and Bandwidth in EQ: what they mean

In Uncategorized on October 7, 2010 at 5:13 pm

If you are reading up on EQ, and wondering exactly what the terms ‘Q factor’ and ‘bandwidth’ mean, maybe this will help.

Q factor controls the bandwidth—or number of frequencies—that will be cut or boosted by the equaliser. The lower the Q factor, the wider the bandwidth (and the more frequencies will be affected).


Low Q factor in Logic

Low Q factor of 0.35 results in a wide bandwidth


The higher the Q factor, the narrower the bandwidth (and the fewer frequencies will be affected).


High Q factor in Logic

High Q factor of 3.10 results in a narrow bandwidth


Most software-based EQ programs have a Q factor range of somewhere around 0.10 to 100; however, only a very small part of this range need be used.

Below is a partial list of Q factors paired with their approximate ‘width’ in octaves:

0.7     = 2 octaves
1    = 1 1/3 octaves
1.4     = 1 octave
2.8    = 1/2 octave
4.3     = 1/3 octave
8.6     = 1/6 octave

As you can see, even a Q as high as 4.3 has a very narrow bandwidth. Qs of this width are very useful for ‘surgical work’ (e.g. removing noise artifacts, such as clicks or string noise), but should be used very sparingly, as their over-use can cause the track to sound very unnatural.

Most boosts and cuts should be carried out with a much gentler Q factor, of somewhere between 0.6 and 1.0, as this tends to result in a much more natural sound.

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