[sdiy] Phase shifts and instantaneous frequency
harrybissell at wowway.com
harrybissell at wowway.com
Wed Jul 16 18:44:54 CEST 2008
I see. That point (at the least common multiple) is the same
as any other zero cross, and no more interesting (although it ~does~
occur at the LCM between the two waves).
Ian's point is that the energy in the air at any point in time is the
same (if I understood him corretly). Lets say that there is 1W of 100 Hz
and 1 watt of 201 Hz... the total energy is 2W. It isn't 1.9W or 2.1W
and that amplitude shift is not what makes you hear the beats. Although you
can 'see' a pattern in Ton's figure, you don't hear it because the amplitude
has changed.
The beats are produced by a non-linear mechanism in your ears, you are hearing
an artifact that the instruments say does not exist...
The only tones that can have complete cancellation are the exact same
frequency, 180 degrees out of phase.
Now lets talk about "binaural beats" next :^)
H^) harry
On Wed, 16 Jul 2008 17:03:12 +0100, cheater cheater wrote
> Harry,
> they cancel only at a certain instantaneous moment.
> Other than that single point in time, the cancellation is incomplete.
> They also are perfectly in phase only at a single point in time.
> But between those two points the cancellation will engage smoothly.
> That's why you hear beating.
> Those two points are 1 second apart.
> That's why the beating you hear is at 0.5 Hz.
>
> Don't know what annoyed Ian so badly there.
> Maybe he wasn't happy with the way I tried explaining this.
>
> Cheers
> D.
>
> On 7/16/08, harrybissell at wowway.com <harrybissell at wowway.com> wrote:
> > I'm still not getting it...
> >
> > cancellation would mean that for a period of one cycle
> > there is zero output signal (voltage, sound pressure, whatever).
> >
> > I don't see from Tom's example that this ever goes to zero.
> >
> > Of course it will cross zero but even a single sine wave
> > will do that periodically... I'm sure that isn't what you mean.
> >
> > H^) harry
> >
> >
> >
> > On Wed, 16 Jul 2008 15:14:50 +0100, cheater cheater wrote
> >
> > > They will cancel after LCM(1/200, 1/201) seconds.
> > >
> > > Ian:
> > >
> > > Scientific qualifications: have started studying maths in the
> > > maths-phys department at 17 years old and studied since.
> > >
> > > Why am I questioned about this?
> > >
> > > If there's something you don't understand, ask, but please don't make
> > > it sound like I'm making stuff up?
> > >
> > > ...
> > >
> > > On 7/16/08, harrybissell at wowway.com <harrybissell at wowway.com> wrote:
> > > > You said "cancellation is incomplete" ???
> > > >
> > > > That implies that there is some point at which the
> > > > cancellation is complete. They will never cancel.
> > > >
> > > > (I have not seen Tom's picture yet, so maybe I'm still
> > > > not understanding what you mean by cancel...)
> > > >
> > > > H^) harry
> > > >
> > > >
> > > >
> > > >
> > > > On Tue, 15 Jul 2008 22:07:46 +0100, cheater cheater wrote
> > > >
> > > > > Harry,
> > > > > wrong,
> > > > > the 201 Hz partial and the 100 Hz partial start out at phase 0, but
> > > > > after some time they'll be exactly out of phase, at which point they
> > > > > cancel.
> > > > > Until that happens, the cancelation is incomplete and goes from
> > > > > minimum to maximum.
> > > > >
> > > > > The beating is 0.5 Hz because the lenght of a 200Hz wave is half of a
> > > > > 100 hz wave's lenght. Or, the other way around, two lenghts of the
> > > > > 201Hz wave are the lenght of a single 100.5 Hz wave. You should
> > > > > experience beating at 0.5 Hz, so of a lenght of 2 seconds, which you
> > > > > can clearly see on Tom's picture.
> > > > >
> > > > > What you don't experience is the fact that you should be hearing a
> > > > > 0.5Hz fundamental instead of 0.5Hz beat *if your ears were perfect*.
> > > > >
> > > > > Whether or not laws of physics were written down already when you
> > > > > were born, doesn't say that they did not exist. :P
> > > > >
> > > > > Cheers
> > > > > D.
> > > > >
> > > > > On 7/15/08, harrybissell at wowway.com <harrybissell at wowway.com> wrote:
> > > > > > Remember that Ian has assumed SINE waves of 100Hz and 201Hz.
> > > > > > they will NOT beat, because there are no harmonics at all
> > > > > > (so nothing to beat).
> > > > > >
> > > > > > You need a non-linear mixer, which the ear provides.
> > > > > >
> > > > > > There may be something of the 'missing fundamental' detection
> > > > > > that human beings have. The 100Hz and (presumed) ~almost~ second
> > > > > > harmonic might give some perceptual effect.
> > > > > >
> > > > > > I'm just trying to set this straight before Ian comes back and
> > > > > > spanks you. You know that Ian was born before Physics books
existed...
> > > > > > at least those printed with movable type... :^P
> > > > > >
> > > > > > H^) harry
> > > > > >
> > > > > >
> > > > > >
> > > > > > On Tue, 15 Jul 2008 15:00:54 +0100, cheater cheater wrote
> > > > > >
> > > > > > > No, the beats are a normal physical phenomenon. Back to physics
> > > > > > > books, Ian ;)
> > > > > > >
> > > > > > > The original thread's question was about a constant phase
> > > > > > > relationship - not a variable one. Of course you can hear a
variable
> > > > > > > phase relationship, which is called pitch bending. :P
> > > > > > >
> > > > > > > Cheers
> > > > > > > D.
> > > > > > >
> > > > > > > On 7/15/08, Ian Fritz <ijfritz at comcast.net> wrote:
> > > > > > > > You can *easily* demonstrate to yourself that differences
in phase
> > > > are, in
> > > > > > > > fact, audible. To do this, make a signal with two sine
waves at 100
> > > > and 201
> > > > > > > > Hz. This is a signal with a slowly varying phase
difference between
> > > > the two
> > > > > > > > components. If the phase differences don't matter, then you
> > will hear a
> > > > > > > > steady tone. If they do matter, then you will hear beats. In
> > fact, you
> > > > > > > > *do* hear beats. Yes, you can easily detect phase differences
> > > > between two
> > > > > > > > tones. (I learned about this from one of the websites I
ran across
> > > > during
> > > > > > > > our previous discussion of this topic.)
> > > > > > > >
> > > > > > > > What's going on? The beats are a result of nonlinear
mixing in
> > the ear!
> > > > > > > > They do not occur at low volume levels, or if the signals are
> > presented
> > > > > > > > separately to each ear. You can easily demonstrate this to
> > yourself,
> > > > also.
> > > > > > > > The nonlinear mixing produces a difference tone at 101 Hz,
which
> > beats
> > > > > > > > against the 100 Hz signal.
> > > > > > > >
> > > > > > > > Try it!
> > > > > > > >
> > > > > > > > Ian
> > > > > > > >
> > > > > > > >
> > > > > > > > _______________________________________________
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> > > > > > > >
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> > > > > >
> > > > > >
> > > > > >
> > > > > > Harry Bissell & Nora Abdullah 4eva
> > > > > >
> > > > > >
> > > >
> > > >
> > > > Harry Bissell & Nora Abdullah 4eva
> > > >
> > > >
> > > _______________________________________________
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> >
> >
> > Harry Bissell & Nora Abdullah 4eva
> >
> >
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Harry Bissell & Nora Abdullah 4eva
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