Just what is "rumble", exactly?

[rasputin1963]

Take a look at this screencap of a FFT audio spectrogram.    It's a depiction,  in two channels,  of the 1967 Monkees recording,  "Daydream Believer",  imported  as an internet-acquired   MP3.

 

There is considerable sonic data,  apparently,   present below the 20Hz mark,  thought to be the lowest threshold of human hearing.

 

This is what they call "rumble",  correct?    Just what IS rumble,    and where along the recording's lifetime was it acquired?   Sound actually present in the 1967 recording studio?     Present in the master tapes after the song was freshly recorded?     Or introduced much later,  during some other format transformation?    What caused it?   Can that data be safely deleted---  without affecting the sound of the recording---     or is it actually contributing "something"  audible or palpable?  

 

Thanks,  ras

 

[sailorman]

My understanding of rumble, is that it is a very low frequency noise introduced by a turntable platter.   Better turntables had lower rumble specs (along with better wow and flutter specs).   I have an old '71 Thorens turntable with a heavy cast aluminum platter, and it has very little rumble compared to a less expensive B&O turntable I have, with a pressed aluminum turntable.

[MikeRivers]

You don't always hear the rumble, depending on its frequency and amplitude, but it modulates the desired audio signal and creates intermodulation distortion that isn't harmonically related to the source. It can happen electrically or it can happen mechanically (at the loudspeaker).

A flat spot on a drive roller can be heard as a thump each revolution. More nasty is what's known as "cogging," where the motor doesn't turn smoothly but rather, jumps a few degrees many times through a full rotation. A heavy turntable will usually smooth that out, but some don't do as good a job as others.

 

[Kotch]

Surely any low-frequency rumble on the original tape would have been filtered out when it was mastered for vinyl? So if the mp3 was taken from vinyl, then I'd say the rumble is probably not part of the original recording.

Even if the mp3 came from the original tapes, any rumble present wouldn't have been audible in the monitors during the session, so it wouldn't be anything that was intended. I suspect that, on old analogue gear without all the fancy spectral analysis, you might not have noticed it at all except if you tried to run the mix through a compressor and started getting weird artifacts.

 

[MikeRivers]

 

---

Kotch wrote:

 

 

Surely any low-frequency rumble on the original tape would have been filtered out when it was mastered for vinyl? So if the mp3 was taken from vinyl, then I'd say the rumble is probably not part of the original recording.

Even if the mp3 came from the original tapes, any rumble present wouldn't have been audible in the monitors during the session, so it wouldn't be anything that was intended. I suspect that, on old analogue gear without all the fancy spectral analysis, you might not have noticed it at all except if you tried to run the mix through a compressor and started getting weird artifacts.

---

 

You can high-pass low frequency noise (trucks, floor resonance from foot stomps, etc.) on the way to the mastering lathe, but the lathe turntable can also introduce rumble that's actualy cut on the lacquer master.

It's true that they didn't have cheap spectral analysis in the old days, but they could see the woofer cones move at low frequencies that they know they didn't intentionally record. Today there are more recordings made that contain extraneous low frequency noise simply because most people making recordings don't have monitors that can reproduce it well.

People who put MP3 files of records up on the 'net usually don't have $20,000 turntables, so that's where most rumble from this source is introduced.

[blue2blue]

Unwanted VLF from tracking was probably caught at better cutting houses. Even if you didn't have the repro to catch it at the cutting station, you'd almost certainly have a scope (at least after the stereo cutting era began, not sure about before that... can it be I'm not old enough to know something? Dang.) At the cutting sessions I was present at, bass was always a concern. And, indeed, come to think of it, I do remember at least one of the ME's chopping the bottom because of LF problems. Seems I recall making a mental note to check my lows after that... but then realized most studios I was working in didn't even have proper spectral analysis.