boost bass and treble online
Boosting bass and treble looks like moving two faders, but the result depends on where each filter cuts and how much headroom is left before the digital ceiling. The tool runs 3 biquad filters in series (bass: 40 to 500Hz lowshelf, mid: 300 to 6000Hz peaking, treble: 1000 to 14000Hz highshelf), each adjustable from -15 to +15dB, and recomputes a compensation gain whenever the boost threatens to pass -1dBFS.
The mid cut removes the boxiness typical of a small room, and the boost at 5000Hz brings back presence without adding hiss.
It isolates roughly the 300 to 3400Hz band that traditional digital telephony (G.711) transmits, the aggressive cut at both ends is what makes the voice sound "phone-like".
Without auto-gain, -3dBFS plus a 7dB boost would pass 0dBFS and distort, the calculation predicts this before a single sample plays and corrects it with a constant attenuation.
A shelf filter uniformly boosts or cuts everything above (highshelf) or below (lowshelf) a cutoff frequency, it is the bass and treble control of a home stereo. A peaking filter, used here for the mid band, acts around a centre frequency, and how wide that action is depends on Q: a low Q affects a broad range, a high Q makes a surgical adjustment. That is why the mid band has a Q control and the other two do not: Web Audio's shelf filters ignore Q entirely.
Not fully. It has only 3 fixed bands (bass, mid, treble) and only the mid band has adjustable Q, from 0.3 to 8. It works well for quick correction and tonal preview, but surgical notches at one specific frequency or dynamics control still need a dedicated plugin.
That is auto-gain doing its job. It adds the source peak to the largest boost on the curve and, if the prediction passes -1dBFS, applies an attenuation after the filters so the peak does not clip. It is an automatic safety measure, not a bug, a +7dB bass boost on a file already peaking at -3dBFS needs roughly -5dB of compensation to fit.
They are starting points. All of them stay within ±15dB and represent plausible curves (the Phone preset, for example, mimics the 300 to 3400Hz band of classic telephony), but real material varies, so it is worth adjusting each band's frequency and gain after applying a preset as a base.
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