There seems to be a lot of confusion about this. There always is. Mr. Ghost is correct.
Phase and polarity are NOT the same thing. A phase shift is a shift in time. A change in polarity is a change from a positive to a negative, or vice versa.
A simple example would be a 20 Hz sine wave that starts at zero volts, goes to a positive peak then decreases until it crosses zero, going negative until it reaches a negative peak and then returns to zero. Like this little symbol ~ .This is one complete cycle of 360 degrees. This happens 20 times a second so each cycle takes .05 seconds.
If this exact same signal had it's polarity inverted, it would start off going negative instead of positive, but would start at the same time.
If this exact same signal was phase shifted 180 degrees, it would start off going the same direction, but it would do so 1/2 cycle (.025 seconds) later or earlier in time.
Thus the comment about "flip the signal 180 degrees back to positive polarity" is wrong. If you are dealing with a repetitive waveform like a pure 20 Hz sine wave, than a phase shift of 180 degrees will look just like a polarity inversion. Draw a picture and check it out. But music is not so simple.
The comment from Mr. Brie is also a little off base. The recording is not out of phase, it has had it's polarity reversed. When you engage the phase button (should be polarity button)) you do indeed invert the signal. What was going positive will now be going negative, and vice versa. This can also be done by reversing the speaker leads. The common example is that of a drum that produces a very short WHAP sound. Lets say the initiation of the original WHAP sound caused a compression of air. The initial movement of the speaker cone should be towards the listener, which will also compress the air. If the polarity is reversed anywhere along the path form micrphone to speaker, the initial movement of the cone will be away from the listener causing the opposite. Whether this is audible is another story. |
Paulwp,
It seems to me that if we are to have an intelligent discussion about all things audio, then we should use the correct terminology. Since phase and polarity are so frequently misused and confused, I thought I would try to help by offering an explanation. I'm sorry if I used too many words in my attempt to do so. If I offended you by pointing out the error in your post, then I apologize.
P.S. It was 371 words, not 1000. Again, I apologize if this correction offends you. |
Sugarbrie, I think you still have phase and polarity mixed up. I read the web site you point out and he describes it correctly. But your explanation does not mesh with his. I do not intend to be picking on you as most of the other peolpe who have posted to this thread have also used the terms incorrectly.
I am not trying to sound like a know it all here, but there are so many incorrect usages of the terms phase and polarity in this thread that it is hard to keep up. I assume that some are interested in this since there have a number of posts on this. So I'll try one more time.
Out of phase means to be shifted in time. Something occurs earlier or later in time than it is supposed to. You cannot invert phase. The term "phase inversion" makes absolutely no sense. It should be stricken from the English language. You can no more invert phase than you can invert time.
Let's say you play a low note and a high note on an amplified electric guitar at the exact same time. But when it is played back on your stereo, you hear the low note and then the high note a little later. This is a phase shift.
They have been shifted in time. Nothing has been inverted.
Let's say when you play the low note, the initial movement of the speaker cone from the guitar amplifier is out. But when you play it back on your stereo, the initial movement is in. This is a polarity inversion.
If you hook up a battery to your speaker terminals, plus to plus and minus to minus, the woofer will move either in or out depending on how the speaker is wired up. If you reverse the battery, it will move the other way. This is a reversal of polarity. It has nothing to do with phase.
If you record a single cycle of a sine wave and play it back, the cone will move one way and then the other, say first in then out. If you reverse the speaker leads it will move first out then in. This is a polarity inversion. If you leave the speaker leads but hit the phase button on your CD player, It will also reverse to first out then in. This is also a polarity inversion, not a change in phase. The button is labeled incorrectly.
So can you correct for a recording that was recorded with inverted polarity? Yes, definitely. Just reverse the leads on your speakers or hit the incorrectly labeled phase button on your CD player or preamp.
Can you correct for phase shifts? Possibly but it would be very, very complex. |
Bowbow, I understood what you posted and I agree except for the part about DC current. You are right that it does not feed current in both directions at the same time. The current is AC, it alternates. First it flows in one direction and then the other. The rate at which it changes direction is called the frequency. Polarity has to do with which direction it starts.
However, the statement "If you reverse your speaker cables that sound is not in phase. You are hearing an out of phase sound, out of phase" is an excellent example of the point I was trying to make earlier about the misuse of these terms.
It should read: "If you reverse your speaker cables that signal will have it's polarity inverted. You are hearing an out of phase sound with incorrect polarity." I agree that this may end up sounding worse.
I know that some of you are saying enough already, what difference does it make? Well, it makes a huge difference if you are trying to understand what is going on in your system. If I think the woofer is the little speaker and the tweeter is the big one, then we are going to have a very confused conversation about speakers. If you do not understand what polarity means, then how can you hope to determine if your system polarity is correct? On the bright side, you have a 50/50 chance no matter what you do. |
Ok, you guys are right. If major manufacturers like CJ don't use the term correctly, it silly of me to think that I could have any impact. Don Quixote, windmills, that sort of thing.
On second thought, it has always bothered me that the weatherman on TV always says when the sun will rise and set when we all know that it doesn't really rise, it is the rotation of the earth that causes this apparent motion. I better give him a call. |
Whether or not hairs are being split is a matter of opinion. That you are incorrect is a fact. As I stated earlier, a phase shift is a difference in time whereas inverted polarity means a change from positive to negative or vice versa. I don't have any illusion that any of this discussion will change the terminology, but I do think we should understand that phase and polarity are not the EXACT same thing just because audiophiles use the terms interchangeably. If you take a pure sine wave and shift it 180 degrees then it will look EXACTLY the same on an oscilloscope and will sound EXACTLY the same. However, if you take a "signal" containing many different frequencies like music you get a much different result. Since each frequency has a different period, if you shift each frequency by the same number of degrees it will sound different because each frequency is shifted by a different amount of time which results in a waveform that is not the EXACT same thing. That is a reason why speaker crossovers distort the signal. Here is a discussion of it. https://www.passlabs.com/press/phase-coherent-crossover-networks |
When you invert the polarity on your preamp it is not inverting a sine wave, it is inverting a complex musical waveform. The initial WHACK on a drum has much more energy in one polarity than the other. It the initial sound is a compression and you change it to a rarefaction by inverting polarity it may well sound different
Play a pure tone (one frequency) then invert it to see if you can tell a difference. Hint... you can't. |
That said, phase isn’t described in terms of units of delay. It’s described in terms of degrees of rotation for a given moment irrespective of time. The problem with breaking it down as a function of time shift is that time shift would be different for every frequency.
It isn’t a "problem" to break it down as a different time shift for different frequencies, it is the reality and why it causes distortion. While I agree that it is more common to talk about degrees of shift, the degrees don’t adequately describe what is actually happening. If I remember my theory, the cutoff frequency is shifted 45 degrees in a one pole high pass filter. Frequencies below the cutoff are shifted more and those above are shifted less. This shift in time, more for some and less for others, results in a form of distortion BTW we usually describe signals in terms of the time domain (what is the voltage ) or the frequency domain (what frequencies are present) . For instance.. a perfect square wave in the time domain is described by the voltage at any point in time, what you will see on an oscilloscope. In the frequency domain it is described as consisting of a fundamental frequency and an infinite series of odd harmonics of ever decreasing amplitudes, what you see on a spectrum analyzer. If you apply a square wave to a crossover what comes out is no longer square because the different frequencies are shifted in time by different amounts. They are also attenuated by different amounts which along with the change in phase creates something other than a square wave. Never heard of a polarity domain. |
