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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 amped 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?!

There is some truth to the point that the PU is far away from the rattling frets, and therefore doesn't pick that noise up as much. However, the strings do transmit the rattling's transients over their entire length. This is particularly obvious when you're playing with a piëzo pickup into an acoustic-amp: the piëzo bridge is even further away from the frets than a normal magnetic PU, but still transmits quite a lot of rattle.

The main reason why the rattle is so much more pronounced when playing unplugged than plugged is that there's in both cases filtering going on:

• An electric bass is a bad acoustic transmitter, in particular in the range of the fundamentals of the actual notes you're playing. That's because it doesn't have much resonating volume. However, the fretboard has enough area to transmit high frequencies to the air relatively efficiently. So we can say, playing unplugged means your signal comes through a high-pass filter^†. It so happens that the rattle consists almost only of high frequencies, whereas the normal string vibration has very little of those. So, when playing unplugged you hear the rattle well and over only a very quiet reference signal level.


• Magnetic PUs are excellent at transmitting low frequencies to the amp, and if it's a bass amp it should also be good at transmitting those to the air. But most bass PUs have pretty high inductance, and together with the capacitance of the cable (this is assuming a passive bass) that forms an RLC low-pass filter, i.e. the opposite of what you get acoustically. Hence, you'll have a loud low-frequency signal level, but much of the rattley high frequencies filtered away. Moreover, bass amps (especially tube amps) aren't completely linear, they add in some high frequencies of their own through overdrive. This results in psychoacoustic masking, and you may not be able to notice the rattle at all anymore – it's still there, just it stands our much much less then when playing unplugged.

However, the remaining rattle can actually be really useful musically. Active basses can bring this out much better than passive ones, because there's no inevitable filtering by PU+cable. The most extreme use is the slap style, which is all about letting the strings hit the frets real hard; when you do this unplugged you'll hear almost only the percussive clacking noise, and even with a passive bass the effect is still obvious. But at least for me, I think a bit of rattle is also important part of my normal plucking sound, it's quite helpful to bring dynamics out and make your lines audible without needing to crank up higher EQ frequencies (which can easily become annoying).

^†_{Incidentally, with a piëzo PU you'll often also get a high-pass filtering effect, because its impedance is capacitive rather than inductive. That's the main reason why piëzos are often perceived to sound “more acoustic” than magnetic pickups, though really this isn't a property of the pickup types themselves but of the (often not well-designed) circuits they're used in.}

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 will 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.