Another ridiculous question - waveform distorions/harmonics?

[Watchmaker]

Being the rookie that I am, I would like to ask the pros here to lighten the burden of my ignorance. Below are three screen shots of a 1.6 second long section of a bass line. It is the same section at different zoom levels so don't mind the apparent amplitude differences.

Super imposed on the bass notes is another waveform(s) seen as distortion moving through the carrier wave over time, resulting in some cancellation at peaks and troughs. If I scroll zoom in and out quickly, I can see it shifting through different cadences kaleidoscopically, sometimes resolving into very sharp outlines, sometimes looking like a moving phase shift with different densities and multiple complex wave forms. I don't understand what I'm looking at.

My first thought was this was 60Hz running along the bass note and creating a distortion, but there's more going on here than that. Are these sub harmonics??? The after effects of too many years playing rock n roll super star?

Don't worry, I won't go down the bunny trail on "cures." Simply trying to put pieces together. Mods please relocate if I put this in the wrong section.

Thanks again for the generous sharing of experience.

[James Perrett]

Could you post the actual section of that sound file that the waveforms come from somewhere? I've no idea if we are seeing an artefact of your software's waveform drawing or whether there is something real so it would help to be able to examine the sound in software that I'm familiar with.

[Hugh Robjohns]

The first thing to say is to be very careful with assumptions about spectral content derived from DAW waveform displays. They are notorious for their inaccuracy due to compromises in the translation from waveform to pixels. You can get the equivalent of wagon wheels going backwards!

I can't make out timescales on your screen grabs, which means I can't work out the nominal low and high frequencies, but it does appear that you have a low frequency modulated by a High frequency (or vice versa).

Obviously, a bass generates a range of harmonics, but I'm wondering if you might also have some high frequency interference getting in their too?

An FFT spectrum display might shed more light on what's going on. There should be a fundamental bass note with a series of harmonics of decreasing amplitude, changing pitch together on different notes. But is there also a static HF tone or two as well?

[Watchmaker]

Thanks Gents.

I will post a clip on soundcloud tomorrow and share a link. I'm out of the studio again for now. The clip sounds fine. I wasn't playing anything serious, just checking that my clocking issues was resolved.

Hugh, the wagon wheel spokes analogy is spot on. I had never considered the rendering aspect, but also I have never seen such a pronounced image.

más mañana

[Sam Inglis]

Is that a synth bass, or a bass guitar? I'm just wondering if we are seeing an LFO doing its thing...

[amanise]

I've seen that before on a bass guitar, which I've connected up to a channel I've previously used for Vox with a compressor insert still active and not set up for the bass yet. It made a fluttering sort of sound as the notes died away - as the compressor seemed to panic and fibrillate in and out until the noise gate eventually sorted the whole signal out. Setting the compressor properly stopped it. Have no idea whether this is the same thing though - but the waveform certainly looks familiar.

Is it pumping?

[ajay_m]

The human ear operates in the frequency and phase domain, not the time domain. While we often view waveforms in the time domain this can result in misleading information. For example the harmonics that make up a square wave will show a very different looking wave if you shift the phase of some of them but the ear will still hear the same timbre.
Hence you may find feeding the sample through a high resolution fft may give you a more intuitive picture of what you're seeing.

[Watchmaker]

Good morning. Thanks all for the comments. Below is a link to a .wav file on Soundcloud I just recorded for this purpose. My gut says it's just a distraction and nothing to worry about, but I do find it intriguing. My ears tell me it's fine. I'm sure it's something obvious to a properly trained and experienced engineer.

It's a bog standard Mexican P-bass running straight into the Hi-Z input on a Focusrite 8PreX, using Studio One v6, no FX at 48k. Sorry "God rest ye Merry gentlemen" was all I could come up with...and I'm not a bassist so...*edit* the riff is supposed to be in "E" but it's probably out of tune...

I did several takes using different interface inputs in both Logic and Studio One using different signal chains, settling on this as the cleanest for sharing. I did learn my Mark Bass DI out is very dirty and I won't be using that anymore!

Anyway, the waveform artifact is consistent in both S1 and Logic, even when I record in one and view in the other.

I did run spectrum analyzer in both DAWs and wasn't able to identify any obvious problems. One final note, Soundcloud displays a waveform that looks slightly offset. This is not how it displays in either DAW where is shows as being symmetrical across the zero bound.

https://on.soundcloud.com/rfUvYmyWa3J5PqLV8

[Hugh Robjohns]

Thanks for that. I'll try and check it out later today or tomorrow and report back.

[James Perrett]

I did run spectrum analyzer in both DAWs and wasn't able to identify any obvious problems. One final note, Soundcloud displays a waveform that looks slightly offset. This is not how it displays in either DAW where is shows as being symmetrical across the zero bound.

https://on.soundcloud.com/rfUvYmyWa3J5PqLV8

Soundcloud always shows waveforms as offset - it doesn't mean anything.

I notice that the second and third harmonic start at a similar level to the fundamental but they sustain for much longer - particularly the second harmonic. I would guess that you are plucking the string fairly near the bridge. Plucking the string further from the bridge should give more of the fundamental.

[Watchmaker]

I notice that the second and third harmonic start at a similar level to the fundamental but they sustain for much longer - particularly the second harmonic. I would guess that you are plucking the string fairly near the bridge. Plucking the string further from the bridge should give more of the fundamental.

Clearly you know your business. I would never have seen that even knowing the physics of harmonics, the distinction between knowing and knowing... Thanks for the insight! I feel incrementally more aware now

[amanise]

Didn't see anything out of the ordinary in iZoptop - but that just shows a solid block for the waveform. Nothing unusual in the spectrograph view. Maybe a tiny fade out and back in about half way through the clip - but hardly noticeable. Didn't sound phasey or anything. Quite nice I thought. Make it red!

Silly question - does that bass have a battery?

[Watchmaker]

No battery. Just an ol' P-bass. Thanks for taking the time to investigate. It'll probably be related to this video monitor's refresh rate or something arcane and esoteric.

As Joe Walsh said..."Sometimes, I can't help but feelin' that I'm living a life of illusion"

[amanise]

No battery. Just an ol' P-bass. Thanks for taking the time to investigate. It'll probably be related to this video monitor's refresh rate or something arcane and esoteric.

As Joe Walsh said..."Sometimes, I can't help but feelin' that I'm living a life of illusion"

Bless him He is crazy though

[Watchmaker]

so am I!