Resonant Undertones

[Rick Cornish]

OK… this one has me stumped:

I'm recording some solo guitar music. Think solo jazz guitar meets modern classical. Some odd harmonies... some not as odd.

The harmonies I'm playing occasionally produce some strong undertones (octaves below the played notes, even below the range of the instrument), which—as I EQ and compress the tracks—sometimes become more pronounced. The undertones are present on all three tracks (mic, direct, and preamp), though less noticeable on the mic track (my semi-hollowbody guitar doesn't produce much low end acoustically). I'm recording in my studio, which is a purpose-built building with acoustic treatment in the control/recording room and the effect is most pronounced on the direct channels (not to mention it sounds the same on multiple monitors and in mono), so it's not a room resonance. The artifacts are also apparent when listening in other environments as well… anywhere that can reproduce low tones (i.e not an iPhone or laptop speaker).

I already have high-pass filters on each track (MWEQ set around 80Hz). I was able to bring one particularly bad track into RX6 and get rid of most of the undertone artifacts and some of their harmonics, but not 100%.

In this music, odd resonances that would be imperceptible on a full band track are out in the open for all to hear. I'd be interested in any experience you folks may have with this acoustic phenomenon as well as any ideas you might have to further reduce or eliminate these weird artifacts.

Many thanks.

[stubbsonic]

I wonder if those aren't caused by some wave interactions which actually produce those tones in the ear, rather than in the air. If it is happening in your ear, then EQ won't sort it.

I remember as a kid, my friend and I would scream into each others faces and we'd hear a mysterious third person singing odd little melodies in a lower tone.

[Rick Cornish]

I wonder if those aren't cause by some wave interactions which actually produce those tones in the ear, rather than in the air. If it is happening in your ear, then EQ won't sort it.

I remember as a kid, my friend and I would scream into each others faces and we'd hear a mysterious third person singing odd little melodies in a lower tone.

That's an interesting hypothesis. Since I can change the sound of the resonance with the processing I'm applying to the tracks, my suspicion is that it's printing to DP.

[FMiguelez]

I thought undertones can only be produced artificially, i.e. via software.
Can they really occur naturally like that?

[HCMarkus]

I thought undertones can only be produced artificially, i.e. via software.
Can they really occur naturally like that?

https://en.wikipedia.org/wiki/Combination_tone

A combination tone (also called resultant or subjective tone) is a psychoacoustic phenomenon of an additional tone or tones that are artificially perceived when two real tones are sounded at the same time. Their discovery is credited to the violinist Giuseppe Tartini (although he was not the first, see Sorge) and so are also called Tartini tones.

There are two types of combination tones: sum tones whose frequencies are found by adding the frequencies of the real tones and difference tones whose frequencies are the difference between the frequencies of the real tones. "Combination tones are heard when two pure tones (i.e., tones produced by simple harmonic sound waves having no overtones), differing in frequency by about 50 cycles per second or more, sound together at sufficient intensity."

Perhaps revoicing offending chords is the answer...

[Gravity Jim]

I like HC's revoicing suggestion. Although first I would try a different mic. My recording acoustic is a bespoke reproduction of a Gibson J50 (a "big" sounding guitar), and the wrong mic will certainly produce some "wolf tones" of the kind you're describing.

[monkey man]

Dynamic EQ, Rick.

That way you can target, with each available band and however many instances of a plug you require to do this, individually-tailored level reduction for each "offending" combination tone.

Obviously DP has one built-in, but there's a plethora of 3rd-party options out there including Waves and iZotope.

[stubbsonic]

When you have two tones that are almost in tune, they produce "beats" as the waveforms drift into phase (louder) and out-of-phase (softer). Piano tuners use this phenomenon to tune pianos. As the two tones go further out of tune, the beats frequency increases until it produces it's own tone.

As I understand it, that's the mechanics of the combination tone described by the wikipedia entry above. You can get rid of the that combination tone (i.e., beats oscillation) by eliminating one of the real tones, i.e., dialing out the one of the real-tone frequencies that are causing the problem. If A + B is producing C, you can't dial out C, you have to dial out A or B. But if A and B are moving around a bit, it won't be that simple.

I kind of wonder why it isn't a problem more often! I often I hear it when guitarists try to play more complicated chords (besides power chords) with distortion on.

[HCMarkus]

I often I hear it when guitarists try to play more complicated chords (besides power chords) with distortion on.

One of the really cool things about distortion! In context, those strange tones can be so raw and powerful.

[stubbsonic]

Agreed.

[Rick Cornish]

Guys.....
Thanks for lending me your brain cells… all suggestions most appreciated!

To respond to a couple comments/ideas…
• No distortion here… even though I do have a preamp in part of the chain, this is clean, natural sound all the way.
• No re-voicing allowed! Every note is written and the voice leading between tones is essential to the composition (think classical guitar music). (i.e. no campfire chords in this one!)

An engineer friend of mine was over last night and suggested it might be an acoustic phenomenon within my guitar. Something vibrating (loose pickguard, loose pickup, etc.), or simply a weird cavity resonance. I spent much of the day chasing those issues. Still working on it. Will report back if I figure it out.

[mikehalloran]

How do you tune? If harmonics are involved, use an electronic tuner to set equal temperment.

If an electronic tuner, "sweeten" (retune) some of those imperfect intervals to the key you are playing.

I normally address this by insisting on electronic tuners and recommending that smaller guitars be used. High pass filters help but a big rosewood dreadnaught plays havock with the bottom end. Keeping it out of the way of the bass can be difficult.

[Rick Cornish]

How do you tune? If harmonics are involved, use an electronic tuner to set equal temperment.

If an electronic tuner, "sweeten" (retune) some of those imperfect intervals to the key you are playing.

I normally address this by insisting on electronic tuners and recommending that smaller guitars be used. High pass filters help but a big rosewood dreadnaught plays havock with the bottom end. Keeping it out of the way of the bass can be difficult.

Great question! Though I spent several years emulating Johnny Smith with low-D tuning, everything I'm doing now uses standard tuning. In the studio, i use a Polytune clip-on, which I find to be the most accurate and occasionally re-tune for specific notes.... like a piece that ends with a held octave with a 5th (G-D-G) and needs to sound without the slightest beating.

Before I started recording this project, I went to slightly heavier strings and had my guitar tech tweak the action and intonation to within an inch of its' life.

As for the smaller guitars comment, my Howard Roberts Fusion III has a smaller face than an ES335, but is slightly deeper and has a solid block of Chromite running down the center.
https://www.guitar-list.com/gibson/elec ... fusion-iii

[buzzsmith]

I remember recording 3 female singers with outstanding pitch. If they were singing a unison, there occasionally would be a ghost octave above!

On a related note, I had a sax guy come by the other day and his "A" (a minor sixth above Middle C) sounded out of tune with the track which was recorded at A=440. Auto tune and the pitch blobs within DP showed him dead on, but it sounded sharp to our ears!

We looked at the overtones within Melodyne and saw no anomalies. Slightly adjusted him down a few cents and all was pretty cool.

No idea why this was an issue.

Buzzy


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[Rick Cornish]

I remember recording 3 female singers with outstanding pitch. If they were singing a unison, there occasionally would be a ghost octave above!

I heard stories of the Mamas and Papas who strived to produce this overtone voice on their sessions...

According to Denny Doherty, he and his golden throated colleagues gave a name to the sound synergistically acquired when their voices blended; they called it Harvey, "an overtone, a fifth voice that was created when the four of us sang together."

http://www.theatermania.com/new-york-ci ... _3409.html

The phenomenon I'm experiencing is more like a wolf tone, though not exactly, as a wolf is a resonant frequency in a (usually string) instrument that sounds sympathetically when the same note is played. In my case, it's an octave or two lower, possibly caused by the vibration of something on or inside my guitar.

Planning more testing tomorrow.