Post
by Nick Sevilla » Fri Jun 01, 2012 11:50 pm
One thing on "absolute" phase, not to be confused with polarity.
Usually, when you strike an instrument, or excite it into making the sound, it wil normally have some part of it which moves, and its' movement causes the air on its' surface to move away from the instrument, which is what we call the "sound" transmission.
Typically, whatever this initial mechanical movement IS, we want the speakers at the final end of our signal chain to move in the SAME direction.
So, imagine a drum skin, which when struck by a beater, moves outwards away from the beater, away from the foot which struck it. This is looking at the drum skin from in front of the kit.
We would call this initial movement the initial excitation phase of that drum skin.
If we are to use this drum skin in a traditional musical mix, we would imagine this drum skin to be in the imaginary "front" of the listener, and we would make sure that the speaker reproducing this sound will move in the SAME direction when the electrical signal reaches it, matching that absolute phase of the insturment.
In contrast, if an instruments' initial mechanical movement is AWAY from the intended listener, then we would expect the speaker to move again, in the same direction of the mechanical movement which created the sound.
Now for the fun, very simplified explanation of Polarity in an electrical wire:
Polarity has to do with the ELECTRICAL properties of a balanced electrical signal travelling through a balanced wire, such as we have in an XLR 3 pin cable. In a system, we typically decide to assign pin 1 to ground, pin 2 to "hot" or positive voltage swing, and the pin 3 to the negative voltage swings. These two voltages, although are complete waves within the wire, are only used to allow a longer cable run, by splitting the positive and negative portions of the original waveform, into two polar opposite voltages, which travel at the same time down the wire, and reject RF inteference which may exist in the air around the wire. The two voltages are usually half the amplitude of the original signal.
Once these two polar opposite signals reach the mic preamp, they are again combined and sent down, combined back into the original signal and amplitude, then amplified within the preamp as much as necessary for further processing. Typically the reconstructed signal is turned into a DC signal flow, with only a voltage wire and ground, for most applications, which allows for very small components to process it to be used. Like our modern transistors.
As you can read from the above, Polarity has nothing to do at all with the sound itself, it is only concerned about what voltages are going down a wire.
I hope this clears some misconceptions on what is going on.
Cheers
Howling at the neighbors. Hoping they have more mic cables.
