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Bass tuning with volume

Member for

7 years 7 months

I've had this before, but it always resolved itself, but I've proved it happens.

When I play my fretless bass if the volume level has to be high on stage, I play flat. I have no choice with the fretted bass, but I'm often convinced I am perfectly out of tune. Doing a Drifters show the other night and it's a quiet stage - everyone on in-ears, but the bass had a big and loud amp. In the wings we could hear the sound from the FOH and the direct bass and the bass was very out of tune sounding - E was half way between E and F - that bad. I asked a couple of others who said exactly the same - it was terribly out of tune, but the guy was good so this seemed 'wrong'. I recorded a bit on my phone and the bass is perfectly in tune. 

Here's the question. Why were we hearing the VERY loud bass sharp - easily 50 cents worth, when the phone proves it was in tune? What mechanism is changing the pitch we think we were hearing? To us, live - hearing the very loud bass amp from maybe ten feet, it was terrible, but the phone proves it was not. Is this just me and a lucky/unlucky two others, or a real phenomenon?

Comments

Member for

7 years 7 months

paulears Mon, 08/16/2021 - 14:26

Surely not? The relative speed of sound doesn't change with volume, it's the speed of sound plus or minus the speed of the source towards or away from the listener. The amp, and our ears were fixed. There must be some mechanism that makes it sound out of tune because it's excessive in level. Clearly in his ears, pitch sounded fine - but to us it wasn't, yet the phone said it was fine? I can't think what is going on?

Member for

7 years 7 months

paulears Tue, 08/17/2021 - 04:04

The clip is the evidence that the using was correct - the phone recorded it totally as it was - singers, keys and bass all in tune - no issues. Stage side, so close to the bass amp, we distinctly heard the bass sharp - but it wasn't, so it is a volume related issue that make pitch appear to raise. 

It cannot be anything at all to do with Doppler shift. This requires distance to reduce raising the pitch. Distances were static and did not change. Doppler has no volume component - in fact it's totally independent of volume as the classic police car siren always starts quieter than it is when the police car passes and the frequency starts to drop - Doppler is a red herring here. 

I'm thinking about the ears proactive mechanism with the alteration of the anvil/stapes angles. It copes with volume - but in this example, the keys and voices were flat compared to the bass. We all had one ear with a foam plug, but the other open but covered by non-isolating headsets. So is this related to time of arrival and level between the local bass and the more distant keyboard and audience PA sound? I really don't know, but the effect was obvious to two people - both close to the bass amp.

Member for

15 years 4 months

Boswell Wed, 08/18/2021 - 04:55

Late to the topic, sorry. I have been away for a few days.

This is not a fault with the instrument or the audio equipment - it's a well-known psycho-acoustic effect that perceived pitch varies with sound intensity (loudness). However, the usual effect is that higher frequencies (e.g. >2KHz) sound sharp at higher intensities, where lower frequencies (e.g. <1KHz) sound flat as the intensity is increased.

These results are applicable to single-frequency tones (sinewaves), so do not necessarily apply to real music waveforms. The higher harmonics of a bass guitar note fall into the more sensitive range of human hearing, and thus could sharpen the perceived pitch of a bass note.

A quote from hyperphysics.phy-astr.gsu.edu:

Effect of Loudness Changes on Perceived Pitch

A high pitch (>2kHz) will be perceived to be getting higher if its loudness is increased, whereas a low pitch (<2kHz) will be perceived to be going lower with increased loudness. Sometimes called "Stevens's rule" after an early investigator, this psychoacoustic effect has been extensively investigated.

With an increase of sound intensity from 60 to 90 decibels, Terhardt found that the pitch of a 6kHz pure tone was perceived to rise over 30 cents. A 200 Hz tone was found to drop about 20 cents in perceived pitch over the same intensity change.

Studies with the sounds of musical instruments show less perceived pitch change with increasing intensity. Rossing reports a perceived pitch change of around 17 cents for a change from 65 dB to 95 dB. This perceived change can be upward or downward, depending upon which harmonics are predominant. For example, if the majority of the intensity comes from harmonics which are above 2 kHz, the perceived pitch shift will be upward.

For the case of the bass guitar, an interesting test might be to put a variable LP filter in the bass guitar channel and see whether the perceived sharpening effect varies as the higher frequencies are gradually removed by progressively lowering the filter cut-off frequency.

Member for

12 years 1 month

kmetal Wed, 08/18/2021 - 22:49

http://www.linkwitzlab.com/…

 

The link explains doppler distortion in a speaker, something i just became aware of a few weeks ago. I don't even really understand it yet, but it seems to be some form of modulation in upper frequencies, caused by a speakers back and forth motion.

Not sure if this applies to Paul's situation but its an intersting effect. With a big loud cabinet possibly on wheels and a wooden stage, there is alot of opportunity for motion of the speaker/cabinet. If the bassist is not running a crossover then the woofers would be operating at full range.

A vibrating stage could send vibrations right thru the body/ears as well. Plus mains, and monitors. Between all those sources there seems to me to be quite a bit of opportunity for modulation and phase stuff, in addition to what Boswell is talking about.

 

Again i dont know how to quantify the effect, but its interesting.

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