"Clean" boost a hoax?

[earthtonesaudio]

Those two phono preamps still remain "clean boosters" in the words meaning.
Here`s wondering if the OP meant to say: "clean boost", or rather: "clean booster" ?

I guess what I meant was the way people talk about their boost pedals, with the buzzwords like "transparent, fat, liquid" etc.  Probably all just ways of saying it "sounds louder" but without any quantitative data to back it up... which would be impossible anyway considering there's no standard guitar, amp, speaker, and on and on.

My original point was that any sound, electronic or not, is perceived differently at different volumes, and therefore you can't change volume while retaining the exact same *perception* of harmonic content/pitch/timbre, that sort of thing.

It's pretty clear that most people on this forum understand all that, but the ad copy isn't necessarily written by people who understand the physics, so the average guitarist probably has a very different idea of what is possible in terms of "clean boost" compared to people here.

I've really enjoyed hearing everyone's take on the subject.  Sorry if I caused any annoyance at resurrecting an old topic.

[ayayay!]

I think it's fun.  So what if we're rehashing an old one?  Sometimes you can find a twist or learn something new.

[JDoyle]

My original point was that any sound, electronic or not, is perceived differently at different volumes, and therefore you can't change volume while retaining the exact same *perception* of harmonic content/pitch/timbre, that sort of thing.

There was one study, which I can't remember, that showed that perceived PITCH changes with loudness! That is amazing...

[petemoore]

  Boosts don't boost anything without an amp 'n speaker.
  At the point at which they can boost, they have become only part of the tone or distortion equation.
  Most of the guys makin' SS amps have figured out that a 'boosted' one might sell because of it...hence 'boosting' that may seem like a 'double boost'...ie noisey and perhaps rough sounding.
  If you have a tube amp that doesn't 'rail out' [or get cranky sounding] on it's own, a booster might find the distortion in the amplifier which otherwise would not be found.
  As soon as 'something' does 'something' to the sound, there will be 'other' things happening also...what those are of course vary from setting to setting, case to case, as well as other variables, much too varied and complex to talk about in any general sense.
 

[Mark Hammer]

There was one study, which I can't remember, that showed that perceived PITCH changes with loudness! That is amazing...

It's actually not a "study" as such, but a basic principle of hearing, and the reason why the pitch of notes seems to go off and upwards when listening to a song that fades out.

As I understand it, the reason why it happens is that pitch is partially detected by where in the cochlea different wavelengths peak or "break".  At lower amplitudes, the wave breaks in a more precise localised manner, and the acoustic signal is precisely encoded based on where in the cochlea the maximum stimulation occurs.  As the intensity/amplitude increases, a larger area of the cochlea is stimulated.  Think of it like the difference between trying to play piano with your knee vs with your big toe.  Hard to play a specific melody with your knee.  It's more like hitting "ranges" of notes.

The actual precision of hearing is constructed within the ear via something called "lateral inhibition".  Here, those nerve cells which are most strongly stimulated suppress the output of adjacent cells that are less strongly stimulated, mimicking what would have happened if the actual physical stimulation were more precise.

A good example of this is touch.  Right now, close your eyes and press the outside of your forearm with your index finger or with a pen.  You can pretty much tell where you are being touched.  Okay, now open your eyes and look at what happens when you press that area.  You can see that, since your skin is all connected, touching one spot also provides some displacement and stimulation of adjacent areas.  Still, you feel it as a precise touch in a specific area.  The feel it this way because the place where you are pressing most suppresses the output of areas adjacent to it such that....
_           _
  \        /
    \    /
      \/

artificially becomes...

___   ____
     | |
     | |
      \/

Lateral inhibition will only take you so far, though.  Once the auditory stimulation is intense enough to cover a broader area along the cochlea such that lateral inhibition can't produce the needed precision, this results in the pitch being "heard" differently, and somewhat lower than it actually is.  As the volume fades out, the normally-occurring lateral inhibition can now begin to impose more precise frequency detection, and the pitch seems to drift upwards as that precision kicks in and also as the nerve cells which had been exhausted are able to respond with appropriate sensitivity.  It's a bit like the phenomenon where you go from bright lights to pitch black and your vision seems to recover with time.  Different mechanism, but similar phenomenon.

Years ago I played with a bass player who was pretty much tone deaf.  Whenever he would tune, he thought that turning up would help him tune more accurately.  I kept trying to explain to him that it was actually contributing to his poor intonation.  He would have none of it.  After all, if you're trying to nail down an E, making that E louder should make it easier to identify, right?

[JDoyle]

There was one study, which I can't remember, that showed that perceived PITCH changes with loudness! That is amazing...

It's actually not a "study" as such, but a basic principle of hearing, and the reason why the pitch of notes seems to go off and upwards when listening to a song that fades out.

As I understand it, the reason why it happens is that pitch is partially detected by where in the cochlea different wavelengths peak or "break".  At lower amplitudes, the wave breaks in a more precise localised manner, and the acoustic signal is precisely encoded based on where in the cochlea the maximum stimulation occurs.  As the intensity/amplitude increases, a larger area of the cochlea is stimulated.  Think of it like the difference between trying to play piano with your knee vs with your big toe.  Hard to play a specific melody with your knee.  It's more like hitting "ranges" of notes.

The actual precision of hearing is constructed within the ear via something called "lateral inhibition".  Here, those nerve cells which are most strongly stimulated suppress the output of adjacent cells that are less strongly stimulated, mimicking what would have happened if the actual physical stimulation were more precise.

A good example of this is touch.  Right now, close your eyes and press the outside of your forearm with your index finger or with a pen.  You can pretty much tell where you are being touched.  Okay, now open your eyes and look at what happens when you press that area.  You can see that, since your skin is all connected, touching one spot also provides some displacement and stimulation of adjacent areas.  Still, you feel it as a precise touch in a specific area.  The feel it this way because the place where you are pressing most suppresses the output of areas adjacent to it such that....
_           _
  \        /
    \    /
      \/

artificially becomes...

___   ____
     | |
     | |
      \/

Lateral inhibition will only take you so far, though.  Once the auditory stimulation is intense enough to cover a broader area along the cochlea such that lateral inhibition can't produce the needed precision, this results in the pitch being "heard" differently, and somewhat lower than it actually is.  As the volume fades out, the normally-occurring lateral inhibition can now begin to impose more precise frequency detection, and the pitch seems to drift upwards as that precision kicks in and also as the nerve cells which had been exhausted are able to respond with appropriate sensitivity.  It's a bit like the phenomenon where you go from bright lights to pitch black and your vision seems to recover with time.  Different mechanism, but similar phenomenon.

Years ago I played with a bass player who was pretty much tone deaf.  Whenever he would tune, he thought that turning up would help him tune more accurately.  I kept trying to explain to him that it was actually contributing to his poor intonation.  He would have none of it.  After all, if you're trying to nail down an E, making that E louder should make it easier to identify, right?

I can hang with most stuff posted here, but this one, wow, I'm WAY out of my league... :-)

Except for the tone deaf bass player, I completely understand THAT!

[Mark Hammer]

It's actually pretty simple....once all the details are filled in.  Here's some of them.

1) If you were to surgically dissect the cochlea and unfurl it, it would look sort of like a very long bowtie-shaped tube.  It is wide at the initial aperture, then gets progressively narrower until it reaches the end of the sensing area and then gets progressively wider.  As near as I can figure it, the progressive narrowing is to conserve acoustic energy as it travels through the cochlea by focussing it.  The progressive widening is to disperse/dissipate the energy so that the cochlea can be a closed container without having any travelling waves bouncing back off the far end of that "tube" and cancelling incoming acoustic energy - essentially the travelling wave has to pass through the cochlea in one direction only, and only once.

2) Along the base or "floor" of the cochlea, you'll find what are call hair cells.  These are the sensory receptor cells that initiate the message conveyed to the brain via the auditory nerve.  Key to understanding the "lateral inhibition thing" is the fact that there are several waystations between that first cell and the point where the auditory message starts being processed. 

3) The hair cells are laid out almost like a keyboard of sorts, such that the frequency of the sound wave is coded by where in the cochlea the wave peaks.  As you move from one end of the sensing area to the other, different frequencies are sensed.  Sensory physiologists refer to this as "spatial" or "place-coding"; implying that the message to be conveyed is coded by where the the stimulation provokes cell firing.  Higher frequency short-wavelength sounds peak closer to the entrance way (makes sense; short wavelength), and lower frequency longer wavelength waves peak closer towards the far end of the sensing part of the cochlea.  I have absolutely no idea if there is any sort of biological "taper" to the arrangement of cells along the cochlea such that there might be greater precision in some frequency ranges than others.  Stands to reason there very may well be.  I just don't know that for a fact.

4) The hair cells themselves are not directly stimulated/provoked by the sound wave.  Rather, there is a membrane directly above them - the basilar membrane - that moves as the sound travels along it.  Think of it like two people holding a long piece of fabric or a bedsheet.  One person gives a quick flip and the wave travels along that piece of fabric for some distance.  As that travelling wave peaks at a point corresponding to its wavelength, it touches the nearby hair cells, thus triggering them and starting the message-to-the-brain process.  Some neurophsyiologists like to think of hearing as actually a very specialized sense of touch for that reason.  That's also why using the skin analogy, as I did yesterday, as a useful way to introduce it, since every part of the basilar membrane is attached to every other part, just like your skin.  It is clear that some general region will be more affected by the incoming sound than another one will, depending on the frequency and corresponding wavelength, but one would be foolish to think that the movement of that membrane would have the sort of precision one finds in a keyboard.  THAT'S why the nervous system needs lateral inhibition - to fake the precision in detection that is not actually built in to the front line of sensory receptors.

5) The "shut-up...you're not loud enough" lateral inhibition mechanism takes place one or two cells further along between the hair cells and the brain.  Imagine several people simultaneously arrive at a doorway that only accommodates one person passing.  The larger fiercer of the the group goes first and closes the door behind him/her.  That's a crude analogy but you get the point.  In actuality, what happens is that branches of the pathway not only go to the brain but spread out laterally to adjacent pathways.  Maybe the appropriate analogy here is to think of a multi-lane highway with one high-speed vehicle bobbing and weaving in a manner that forces other drivers to keep their foot on the brake and slow down or even come to a dead stop.  They're all headed in the same direction, but some vehicles take priority and suppress the movement of those near them.  In this case, we have hundreds, or maybe thousands of hair cells stimulated at the same moment.  All of them now send their message on to the next nerve cell in line, but since some of them are"shaken up" by the basilar membrane moreso than others, their message is stronger and suppresses the output of nearby hair cells when that output shows up one or two cells further along in their journey to the brain.

6) Following up on the two people shaking a bedsheet example,  a gentle shake will result in a smaller part of the sheet/membrane moving a sufficient amount to stimulate nearby hair cells, so the region covered will be smaller.  A big shake results in several things.  First, more cells will be stimulated over a wider area.  Second, nerve cells can only fire so many times a second before they are exhausted and need time to catch up.  If they can't fire, they can't suppress adjacent cells either (the lateral suppression is a component/side-effect of firing), so the capacity for imposing lateral inhibition is reduced under heavy attack.


I suppose you can tell that I find hearing and the biology of the ear utterly fascinating.  Check into it a bit further than my own lunatic ramblings, and I have no doubt you will find it every bit as fascinating.  If memory serves, I think there is a damn good chapter on it in the Audio Cyclopedia.

We now return you to your thread, already in progress.

[earthtonesaudio]

Awesome Mark, thanks for that!

One example that's relatively easy to find of the perception of pitch changing with volume is in live recordings.  When the singer has the monitors loud, the pitch goes off.  If the main speakers are loud too, the audience probably won't notice, but it shows up in the recording when you play it back at lower volumes.  Probably easier to find with older live recordings than it is with newer ones, due to improved monitor technology and in-ear monitors that allow lower on-stage volumes.

[ayayay!]

Mark Hammer may have mentioned this, but goes hand in hand the doppler effect.  Haven't you walked out of a loud venue into a hallway and suddenly everything sounded flat?  The hairs in your ears react differently to different sound pressure (volume) when it's at a higher level.

Same thing when an ambulance goes by and once the horn faces away from you the pitch is suddenly flatter.  That's doppler.  The higher frequencies are still there but attenuate due to surroundings or dissipation, thereby giving the perceived result of the pitch going flatter, but it's really not. 

This is why I always tune live with a very good pedal tuner that mutes.  Otherwise, you may have a hard time tuning it correctly.  If you trust your pedal tuner, then tune it silently and you'll have better results.   

[puretube]

Same thing when an ambulance goes by and once the horn faces away from you the pitch is suddenly flatter.  That's doppler.  The higher frequencies are still there but attenuate due to surroundings or dissipation, thereby giving the perceived result of the pitch going flatter, but it's really not. 
...   

they are not there, anymore, but are moving away from you...
That`s Doppler.

[ayayay!]

Okay Okay, the frequencies that seem to be rolling off still being produced (by the source) was what I meant.  I see what you mean puretube.

(Actually I was trying to edit that repsonse 2 days ago but my session timed out.  Hehe)