It's easy to imagine a 1000hz and a 1200hz generate a 200hz, or a 1200hz and
a 1400hz generate another 200hz, for there is the common divisor. But, say,
will a 500hz and a 900hz generate a 400hz?
xue
-----Original Message-----
From: Richard Dobson
Sent: Thursday, December 06, 2012 1:27 PM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Ghost tone
A "beat" is a small difference frequency, e.g. 1Hz. It will appear on
the scope as a slowly amplutide modutaed signal. High C and E are
harmonics of of middle C (specifically, 4th and 5th), the difference
between those frequencies give the frequency of the "difference tone".
"beat" and "difference" are one and the same, but in the vernacular we
only apply the word "beat" to very small differences which become heard
as tremolo. Literally any two tones presented together will generate a
difference tone. I can't say whether that arises specifically from
non-linearities in the ear, but most certainly it does rise in the ear;
and of course is intensity-dependent.
Both C-E and E-G will generate the same difference tone (middle C) as
the differences between the two frequencies (in just intonation!) the
same. Given 500 partials 30hz apart, they will all conspire together to
generate the mother of all difference tones, reinforcing each other.
In fact, it often happens thet we hear multiple difference tones; it is
almost a recursive process. So given a large number of partials, the
"result" may well be pretty complex, as each partial is different from
each other by some amount or other.
In the case of beats, as those closely separated tones diverge, the beat
frequency rises, until that point (whose proper name I forget offhand)
where the effect degrades to an uncomfortable degree, until eventually
we are aware of two distinct pitches. That trasnisiotn point corresponds
to the traditional lower limit of human pitch perception, e.g. around 20Hz.
If a sound is very loud, it drives the ear into even more non-linear
regions, and if sustained may cause damage. There is a whole range of
frequencies which are peceived as lower or higher according to how loud
they are (you can test this with any sinusoid and a level control), so i
am happy to presume that one way or another the ear is non-linear rather
a lot of the time!
Richard Dobson
On 06/12/2012 13:09, Didier Dambrin wrote:
But in your example, the beating (which I still don't consider as a tone
but that doesn't matter) comes from the tuning of C & E, while in the
audio file all of the partials are harmonics, there are no 2 periods
against each other.
More, they are the same in both halves, the only difference is in the
initial phases, and that's enough to make the ghost tone completely go -
you would never make the beating you describe disappear by toying with
initial phases, as the periods (whether it's 1 big pulse or random
cycle) are exactly the same.
Really, the phenomenon here is not beating IMHO.
-----Message d'origine----- From: Richard Dobson
Sent: Thursday, December 06, 2012 1:44 PM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Ghost tone
There is no reason a resultant tone (or difference tone) has to be low.
I demonstrate this with my flute students all the time in the context of
tuning. Play high C and E on two flutes, say, and the resultant tone
will be clearly heard, hovering around middle C depending on how the
interval is tuned (I lip-bend the E to show the effect especially
vividly). Needless to say, in strict equal temperament, that difference
tone is horribly sharp. A difference tone of this kind is in effect a
"beat frequency" fast enough to be heard as a pitch (a form of amplitude
modulation). An orchestra generates difference tones all the time, most
obviously from the wind and brass sections, and a standard part of the
technique of classical orchestration is to avoid loud small intervals in
the low register, as that will produce the archetypal "muddy" sound.
Setting aside any individual or non-normative differences in auditory
perception, such difference frequencies will always be present (but
might conceivably be masked by other sounds, and of course the
generating notes have to be loud to get the effect clearly).
Record producers even depend in it; music played over very small
speakers outputs little or no true low frequency content; but the ear is
remarkably good at reconstructing virtual bass from the higher partials
that do get reproduced.
On the other hand, the ear has a remarkable ability to block out static
sounds, especially where it is not expecting to experience any, such a
as VLF; the sense of the resultant tone might be easier to pick up if
the pulse wave was generated with vibrato (VLF pitch modulation).
One aspect of psycho-acoustic masking that applies here is that loud
high frequencies cannot mask low frequencies, but a loud low frequency
can easily mask higher frequencies.
The phase-shifted version of the pulse wave can be expected to have an
effect on resultant tones, due to the more or less random local
cancellation effects that may arise.
Richard Dobson
On 06/12/2012 12:13, Didier Dambrin wrote:
not at all (plus I never really heard beat frequency as a "tone",
beating/a detectable period yes, but not a bassy tone)
-----Message d'origine----- From: Richard Dobson
Sent: Thursday, December 06, 2012 12:49 PM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Ghost tone
Isn't this simply the resultant tone (beat frequency)? Given the partial
are approx 30Hz apart, it would make complete sense that the resultant
tone would be in that region. It would be affected by room responses,
and rotating the heard while lisetnting will change the perceived
intensity etc.
Richard Dobson
--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews,
dsp links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp
-----
Aucun virus trouve dans ce message.
Analyse effectuee par AVG - www.avg.fr
Version: 2012.0.2221 / Base de donnees virale: 2634/5439 - Date:
05/12/2012
--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews,
dsp links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp
--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews, dsp
links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp
--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews, dsp
links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp
