Do Negative Frequencies Exist?

futures_untold · Post by **futures_untold** » Tue Mar 31, 2009 11:31 am

Can soundwaves be measured in negative numbers? (Eg, one cycle of a sound would take more than a second to complete?)

Sub infra bass!

(That's what brought down the walls of Jericho!)

magma · Post by **magma** » Tue Mar 31, 2009 11:43 am

No... once you reach 0 there is no oscillation and so no sound. Extreme "infra-bass" frequencies are just small decimal values... you can always have one more decimal place, remember: 0.000000001hz is a very low note indeed

One oscillation per second is 1hz - there's still an infinite number of frequencies between that and 0hz.

twistedol · Post by **twistedol** » Tue Mar 31, 2009 11:48 am

well not really cos time only moves forwards so you have some crazy vortex that sucks sound out of reality. Remeber, Freq = 1/Time so to have a negative freq it'd be like..... just not possible. Negative frequencies SOMETIMES occur in digital sampling theory (for look at digital filters and Aliasing n shit) but bar that, not physically possible yoof.

jarvy · Post by **jarvy** » Tue Mar 31, 2009 12:36 pm

well....

if you input a negative frequency into a sound generator, you will hear the same sound as the positive frequency but the actual sound wave will be inverted (upside down). we may not be able to believe that negative frequencies can exist but this is how computers interpret them....

ketamine · Post by **ketamine** » Tue Mar 31, 2009 2:36 pm

Eops wrote:Bass - pushes the air
Negative Bass - sucks the air ...

LOL But "sucking" the air is just pushing the air in the other direction, so technically its still a positivie action. LOL

thecatinside · Post by **thecatinside** » Tue Mar 31, 2009 5:57 pm

Jarvy wrote:well....

if you input a negative frequency into a sound generator, you will hear the same sound as the positive frequency but the actual sound wave will be inverted (upside down). we may not be able to believe that negative frequencies can exist but this is how computers interpret them....

This shouldn't be a question of belief.

It is just a impossible to have negative frequencies.

martello · Post by **martello** » Tue Mar 31, 2009 6:06 pm

As far we don't know much about black holes, dark matter etc there is nothing impossible.

thecatinside · Post by **thecatinside** » Tue Mar 31, 2009 6:48 pm

Bloody quantum mechanics undoing the laws of classical logic.

ketamine · Post by **ketamine** » Tue Mar 31, 2009 8:23 pm

thecatinside · Post by **thecatinside** » Tue Mar 31, 2009 8:39 pm

nowaysj wrote:Okay, what happens if you move away from a sound source faster than the speed of sound? That is a negive frequency.

As you approach the speed of sound, the frequency will go lower and lower.

When you match the speed of sound, all sound will stop, and as you accelerate beyond the speed of sound you will be hearing negative frequencies.

Well, nothing should happen. If one had a speaker playing a sine wave at 440Hz it should still be playing at 440 Hz no no matter how fast one would run around the speaker allthough it would be observed differently. That's because of Doppler-effect.

Frequencies as a measure of sound are measured on an absolute scale that ends at zero. It could be compared to temperature when measured on Kelvin's scale. It's just impossible to go lower than 0 and still have.

Neuroscientist in me says that if there were negative frequencies they'd still be well below our hearing threshold (20 Hz) which would make it impossible to hear them.

I'm propably talking about different thing here tho. *Waiting for someone with real knowledge on physics (or quantum mechanics

) to correct my simplifications*

ketamine · Post by **ketamine** » Tue Mar 31, 2009 8:40 pm

THIS IS PROFOUND!

"Virtually all basic physical quantities have
an absolute zero, for instance temperature, mass, spatial and temporal distance. This [includes] derived quantities like for instance sound pressure to alternate between positive and
negative values superimposed to the much larger average pressure of air. Likewise, the alternating
electric current can be imagined as a small component superimposed to a larger average motion of
elementary electric charges. The arbitrarily defined alternating components have to have an
arbitrarily chosen reference-point zero. Negative temperature on the Celsius scale relates to the
arbitrarily chosen criterion that water has been frozen to ice."

http://www.fqxi.org/data/forum-attachme ... ginary.pdf

So technicially speaking, the only reason we have "Negative Numbers" at ALL is because a person picked "x" to be zero, so when something falls outside of this, its written as "Negative" but indeed, is NOT in reality.

Therefore, NOTHING really has negatives in reality. It all ends at 0.

Brisance · Post by **Brisance** » Tue Mar 31, 2009 9:00 pm

nowaysj wrote:Okay, what happens if you move away from a sound source faster than the speed of sound? That is a negive frequency.

You will not be able to hear it, because you are moving faster than it, that is all.

djake · Post by **djake** » Tue Mar 31, 2009 9:37 pm

alvin18 wrote:As far we don't know much about black holes, dark material etc there is nothing impossible.

isnt it dark matter

slothrop · Post by **slothrop** » Tue Mar 31, 2009 9:48 pm

Jarvy wrote:well....

if you input a negative frequency into a sound generator, you will hear the same sound as the positive frequency but the actual sound wave will be inverted (upside down). we may not be able to believe that negative frequencies can exist but this is how computers interpret them....

This is precisely what they are (and why noone bothers to talk about them). Think about a sine wave - if f is a positive number then a sine wave with frequency f is given by y = sin(f*x).

If you have a 'negative frequency', g, which equals -f (say), then you get
y = sin(g*x) = sin(-f*x) = -sin(f*x) which is actually exactly the same but 180 degrees out of phase ie it won't sound any different.

Since any waveform is basically a superposition of sine waves, taking them with a negative frequency won't make any difference either - the most you'll achieve is inverting the waveform, which afaik makes no difference to the sound of it.

</maths>

thecatinside · Post by **thecatinside** » Tue Mar 31, 2009 9:48 pm

nowaysj wrote:
Brisance wrote: You will not be able to hear it, because you are moving faster than it, that is all.
Not true. You would be hearing the sound of the past.

Flying around on a supersonic airplane doesn't exactly match my visions of time travel

Do Negative Frequencies Exist?

Do Negative Frequencies Exist?

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