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I could hear the fret buzz when playing bass unplugged. But once plugged through the amp. I could not hear the fret buzz anymore.

1. Why are pickups not picking up the fret buzz?


2. Or do I have to crank up the amp volume in order to hear it?

(*I read this post but still can’t get my head around)

The hard impact of the string on the buzzing fret will take some of the energy from the vibrating string (mostly from the lower frequency energy, as this is the energy represented in the larger-amplitude aspects of the vibration), and convert it into higher-frequency energy that both forms a new pattern of vibration of the string, and also causes the fret and the fretboard to vibrate a little.

You hear those higher-frequency vibrations acoustically - but once they've made their way down the string to the pickup, they will have been converted into lower-frequency energy again due to the natural filtering effect caused by the string's stiffness. So if you're listening to your amp at normal volume, the 'buzz' won't be so noticeable.

However, the fret buzz will be changing your sound a little - reducing your sustain, reducing the maximum volume at which you can play the note, and changing the spectrum of the plucked note.

Bass players sometimes even use the effect of the string rattling against the frets creatively, to create a little more 'growl' in the sound.

As your linked question's answers state - fret buzz is not "seen" by the pickups. The reason is relatively simple: the pickups respond to the vibrations of the string in the vicinity of the pickup. The fret buzz sound is produced by the string vibrating and touching the fret at the extreme of the amplitude (of the vibration). While it's true that a very small bit of overtone is generated due to the effective "stop" caused by brief contact with the fret, nearly all the buzz is at the fundamental frequency of the string (because the fundamental's amplitude is far greater than the overtone series). This means that the fret buzz contributes almost nothing to the net vibration pattern at the pickup; hence no output.

You're hearing the fretbuzz because it's emanating from a fret close to the fretted note. That's nowhere near the pup. The pup only picks up vibrations directly over its poles. So any fretbuzz is heard by you, but not by the pup.

This can be proved by (probably - it happens on a lot of guitars/basses) playing a harmonic that has its node directly over a pup.Usually where fret 24 is or would be. At that point, there's no string movement therefore nothing for the pup to pick up. You can hear the harmonic, acoustically, and if there's another pup, switching that on will make it come through the amp speakers.

That apart - if you are getting fretbuzz, but it's not coming through the speakers - isn't that a bonus?!

Whilst the buzz itself will not come through the amp (for reasons covered in other answers), an imperfectly-fretted note will still sound like an imperfectly-fretted note through an amplifier. It will sound "dead" and will not ring on properly. In spite of the buzz not coming through clearly, the change in tone should be clearly recognisable.

One possibility of course is that you may have a substantial amount of distortion on your FX; or perhaps you have a compressor. In that case, dynamic range compression well tend to make the change in tone and level less obvious. And distortion inherently makes it hard to hear the original sound of the instrument, which is why you're always advised to practise with a "clean" sound.