# phase shift in a signal

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#### neo_star

##### New Member
if there is a phase shift in a signal by 90 degree or 180 degree frm the orginal signal will it sound the same as the orginal signal

For example an audio signal is amplified using an amplifier and the o/p signal is phase shifted by 90 degree or 180 degree frm the orginal signal. My question is will the audio signal sound the same as that of the orginal audio signal.

#### dknguyen

##### Well-Known Member
First of all, you understand that a phase shift is delaying or advancing a periodic signal with respect to time, right? Except instead of saying "Delaying by X seconds" you are normalizing it to the period of the frequency so you say "delaying by Y degrees for a signal of Z frequency". So a 180 degree delay for a frequency with a period of 1 second would be delaying it by 0.5 seconds, but for a frequency with a period of 10 seconds it would be a delay of 5 seconds.

So if you take an audio signal of a bunch of frequencies and just shift every frequency by X degrees, it will sound different since you are actually advancing or delaying each sine wave frequency component by a different amount of time. The different frequencies aren't overlapping the same way as the original signal anymore and it gets all jumbled up.

BUt if you delay each frequency by the right amount though, , the entire signal will sound the same...it just appears sooner, or later in time.

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#### neo_star

##### New Member
so u say that if the signal is phase shifted by 360 degree it will sound the same and anything other than that will sound different.

#### audioguru

##### Well-Known Member
If a sound system has multi channels then all the channels must have the same phase. In a stereo sytem the bass becomes cancelled if one speaker is 180 degrees phase to the other speaker.

You cannot hear a difference when an entire sound system has its phase changed 180 degrees.

#### dknguyen

##### Well-Known Member
so u say that if the signal is phase shifted by 360 degree it will sound the same and anything other than that will sound different.
For a sound that is just a tone (single frequency) it will sound the same no matter how you shift it. BUt for real sounds made of a bunch of frequencies it will sound different in general. The special case where it will sound the same is if you modify the phase shift for each frequency so that the it's shift in time still makes all the other frequencies overlap in the same way.

A 90 degree phase shift, two different frequencies will be shifted by different amounts of time so the sound will change. But, for example, if you shift one by 90 degrees, and you shift the other by just the right amount (which will be different than 90 degrees) you can get the sound to be the same.

I think 180 degrees is a special case where even if you shift all the frequencies by that amount it accomplishes the things I said so the sound doesn't change (it's hard for me to visualize though).

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#### neo_star

##### New Member
For a sound that is just a tone (single frequency) it will sound the same, for real sounds made of a bunch of frequencies it will sound different in general (unless each frequency is shifted by the proper amount relative to how much every other frequency is shifted.

Even with 360 degrees phase shift, two different frequencies will be shifted by different amounts of time so the sound will change. But, for example, if you shift one by 360 degrees, and you shift the other by just the right amount (which will be different than 360 degrees) you can get the sound to be the same.
oh thank you so much for answering my question

#### dknguyen

##### Well-Known Member
oh thank you so much for answering my question
I think i made a mistake about 180 degrees and 360 degrees. They are very special cases where you can shift all frequencies by that same phase shift and the sound will be shifte correctly in time to still sound the same. Shifting 360 degrees changes nothing (obviously) so the sound stays the same. 180 degrees flips all the sine-wave frequencies upside down, but they are still overlapping the same way relative to each other so you still hear the same sound.

But for all other frequencies it jumbles things up unless each frequency is shifted by a different (and correct amount) based on the period of the frequency to get the same shift in time relative to the other signals.

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thanks again

#### tcmtech

##### Banned
Do they make audio systems that can do 90 degree shifting?
I used to have a 1000 watt at the speaker sound sytem in my 84 mercury topaz back in high school.
I Got a warning ticket for a sound ordinace violation.
After that I put a relay in that reversed one subwoofer phase to 180 degrees from the normal setting.
Next time I got pulled over for a "bass related" charge I flipped a switch under the seat that reversed the one sub. the cop walked up. I told him it was that other car at the stop light, and even cranked it up for him.
Hmmm... no thundering Bass coming from this car. I guess it was not you. My mistake, You can go.
If he only knew!

ah... the secret life of a nerd.

#### confounded

##### New Member
After that I put a relay in that reversed one subwoofer phase to 180 degrees from the normal setting.
Next time I got pulled over for a "bass related" charge I flipped a switch under the seat that reversed the one sub. the cop walked up. I told him it was that other car at the stop light, and even cranked it up for him.
Hmmm... no thundering Bass coming from this car. I guess it was not you. My mistake, You can go.
If he only knew!

ah... the secret life of a nerd.

Genuis!

#### audioguru

##### Well-Known Member
The car must have been windy inside.
A pressure wave on one side rushing to a vacuum on the other side then back and forth many times.

#### tcmtech

##### Banned
Oh yea. Little outside noise but big inside air displacement!
I ran free air subs mounted to the back of the seats on 3/4 inch high density partical board. I used the whole trunk volume as a resonator. It put the natural resonace at least 10 times lower than the tuned port or band pass boxes everyone else was using! (Bigger volume = lower resonance frequency. Simple acoustics!)
I cut the seat foam out from the back to get the sound through without dampening it. The seat fabric was al that was in the way.
I put a lot of effort into that system. Everything but the reciever in the dash was hidden. I had a few friends with systems that had everything out in the open to show their stuff off. They all got broken into and stollen or trashed.
The worst I got was a poorly done keying at the mall parking lot on a sunday after noon. I knew the dumb **** that did it too. Monday morning he said: I see your car got keyed. I said: when did you see this? he said: I saw your door this morning. It must have happened over the weekend, huh? (with a grin in his voice.)
I said, no it didnt. I washed it last night. I would have seen it. Its just fine!
(When it got keyed the doors were so dirty the key never actualy got to the paint. I washed it that night to see what damage there was and there was none!)
There was no way anyone ever saw the actual key marks so knew it was him.

He was from rich family too and got everything handed to him. My car sound system beat his easily! It made him way jealous that a poor farm kid had something he couldnt have! (Brains and skills!)

I never rubbed peoples noses in it that I had the best sound system in the town though.
I always showed them how I did it and often got paid well to redo others systems to work better.
Plus that paid way better than the 80 cents an hour my dad gave me for hard labor.

The kid that keyed me? Well I got him back with interest! At a party a few weeks later I shot a half a can of brake cleaner down his intake with the engine running. Any guess as to what that does to the O2 sensors and catylitic converters?
Piss poor mileage and a big non insurance claimable repair bill shortly follows!

Dont mess with us nerds, we use science to fight dirty!

#### Hero999

##### Banned
I think any phase shift will affect the sound if you've got more than one channel.

In theory tow speakers connected out of phase will completely cancel each other but in practise it won't because the coupling won't be perfect. If I understand this correctly, they start to cancel rather than add when the phase shift exceeds 90°, as ±90° the other speaker is neither cancelling or adding to the waveform.

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