[sdiy] Phase shifts and instantaneous frequency

cheater cheater cheater00 at gmail.com
Wed Jul 16 18:03:12 CEST 2008 

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
>  > >  > >  > >
>  > >  > >  > >
>  > >  > >  > >  _______________________________________________
>  > >  > >  > >  Synth-diy mailing list
>  > >  > >  > >  Synth-diy at dropmix.xs4all.nl
>  > >  > >  > >  http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>  > >  > >  > >
>  > >  > >  > _______________________________________________
>  > >  > >  > Synth-diy mailing list
>  > >  > >  > Synth-diy at dropmix.xs4all.nl
>  > >  > >  > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>  > >  > >
>  > >  > >
>  > >  > >
>  > >  > > Harry Bissell & Nora Abdullah 4eva
>  > >  > >
>  > >  > >
>  > >
>  > >
>  > >  Harry Bissell & Nora Abdullah 4eva
>  > >
>  > >
>  > _______________________________________________
>  > Synth-diy mailing list
>  > Synth-diy at dropmix.xs4all.nl
>  > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>
>  Harry Bissell & Nora Abdullah 4eva
>
>

More information about the Synth-diy mailing list