Simple Explanation

The quality factor of a filter, which defines how narrow or wide the range of frequencies the filter affects.

Concise Technical Definition

Q is the quality factor of a filter that defines its bandwidth and resonant properties. The higher the Q, the more resonant the filter, and the narrower the frequency range that can pass through. In audio, Q is the ratio of the center frequency to the bandwidth, meaning that as you increase Q, the bandwidth becomes narrower. This is a key tool in parametric equalizers, allowing precise control over the range of frequencies being boosted or attenuated. Q is also a function of crossover filters, where it is referred to as the "order" of the filter.

Layman-Friendly Analogy

Imagine tuning a guitar string—if you tighten the string (raise the Q), it vibrates more sharply and with a narrower pitch range. Similarly, in audio, increasing the Q narrows the range of frequencies that are affected by the filter, making it more focused.

Industry Usage Summary

Q is an essential parameter in audio, particularly when using parametric equalizers, where it allows precise control over the frequencies that are either boosted or attenuated. For example, a high-Q setting allows you to target a very specific frequency, while a low-Q setting affects a broader range. This is critical for fine-tuning sound in mixing, mastering, and live sound environments. Q is also used in crossover filters to define how sharply the frequencies are separated between different speaker drivers. It is also relevant in speaker design, where Q (specifically, the directivity index) helps determine the suitability of a speaker for certain applications.

Engineering Shortcut

The ratio of center frequency to bandwidth, which controls the selectivity or sharpness of a filter.

Full Technical Explanation

In the context of audio filters, Q refers to the quality-factor, which defines the bandwidth of a filter and its resonant properties. Q is the ratio of the center frequency to the bandwidth, and the higher the Q, the narrower the bandwidth and the more resonant the filter. This is especially useful in parametric equalizers, where adjusting the Q allows engineers to isolate and boost or cut very narrow or wide frequency ranges. Q is inversely proportional to the bandwidth—raising the Q results in a narrower bandwidth. In addition to equalizers, crossover filters also use Q to define their sharpness or order, which determines how sharply frequencies are divided between different speakers. Furthermore, in speaker design, Q is used to measure the directivity index, which compares the direct radiated energy of the speaker to its total radiated energy, helping determine the speaker’s suitability for specific applications.