lagi kong nakikita ang term na phase at phase shifts, so nagresearch ako to find out what it is...medyo malabo parin sakin haha. i don't know what it actually does to the waveform and how it affects the sound. ano ang mag-iiba kapag nagshift ng phase? sorry, siguro napakaengot na katanungan nito...pero okay lang gusto ko talaga malaman. 
kung ayus lang sana, paki-explain in easier terms, kasi nung nagresearch ako, hala, bakit may nakita akong mga functions at formulas. haha.
The beginning--- Sound and Hearing.
What is sound? Sound is a series of physical disturbances in a medium such as air. When an object vibrates, it sends out a series of waves that propagated through the air. Selecting a loudspeaker as an example; when the loudspeaker cones moves forward, it compresses the air in front of it, creating an area in which the air molecules are denser than normal atmospheric pressure (the normal pressure of the air at sea level; 14.7 pounds per square inch). This portion of the sound wave is called COMPRESSION.
When the loudspeaker cones moves backward, it creates an area in front of it in which the air molecules are less dense than atmospheric pressure. This portion of the sound waves is called RAREFACTION. Sound is made up of a series of alternating compressions and rarefactions moving through the air.
When these compressions and rarefactions strike our eardrum, we perceive the phenomenon as SOUND. The greater the change in air pressure above and below the atmospheric pressure, the greater the AMPLITUDE of the sound.
Because most objects vibrate with a periodic back-and-forth motion, or OSCILLATION, most sound waves (nearly all musical sounds) have a periodic repetition.
Using our loudspeaker again as example-- the repetitive compression and rarefaction motion results to pressure change called SINEWAVE ( imagine a letter S na nakahiga), the most basic periodic repetition.
Defining PERIOD, FREQUENCY and WAVELENGTH. The time it takes to complete one cycle of a sinewave is called its PERIOD. The FREQUENCY of a sinewave is the number of periods per second. A sound's frequency largely determines the sound's PITCH, our subjective impressions of frequency. If a wave's period is the TIME it takes to complete one cycle, a wave's WAVELENGHT is the DISTANCE between successive cycles.
Nasan na yung PHASE & PHASE SHIFT mo ?
The term phase describe tha fraction of a PERIOD that has elapsed in a SINEWAVE. Phase is expressed in degrees, with one cycle of a sinewave represented by 360 degrees. Although phase can be measured from any arbitrary point along the sinewave, 0 degrees is usually where the wave begins its positive going crossing.
The term PHASE SHIFT describes a time displacement of the sinewave relative to a fix point. For example, if the sinewave were delayed by half its period, we would say it experienced a 180 degrees phase shift (because one cycle is 360 degrees, half a period is 180 degrees).
Phase can also be describe the time relationship between two or more sinewaves. If one wave is delayed by half a period in relation to a second wave, we say the second wave lags the first wave by 180 degrees. If one wave is delayed by one whole period (360 degrees) in relation to another wave, it as though the phase shift never occured---the wave returned to its original phase relationship with the first wave.
Phase shift has an important consequences when waves are combined. If two waves of equal frequency and the same phase are superimposed, their combination will create a wave of greater amplitude. Specifically, two waves of equal amplitude, equal frequency, and the same phase will yield an increase of 6 decibels (dB) when combined. These waves are said to REINFORCE each other. If, however, one of this waves is PHASE-SHIFTED by 180 degrees, the two waves will CANCEL each other and produce no signal. When one wave is at peak positive, the wave shifted by 180 degrees is at peak negative, producing the cancellation.
In layman's term, this exactly what happens in a system if ONE loudspeaker is connected with the loudspeaker cables REVERSED ( the red amplifier terminal is connected to the loudspeaker's black terminal, and the black amplifier terminal is connected to the loudspeaker's red terminal). For XLR terminations cable user, go figure! Reversing the leads to one loudspeaker "flips" the signal over, making positive into negative and negative into positive. This is similar to a phase shift of 180 degrees. Now, when one woofer cone pushes forward to create a compression, the second loudspeaker's woofer pulls back to make a rarefaction. When the compressions and rarefactions are combined, they cancel; the compressions from one loudspeaker "fills in" from the second loudspeaker, and less sound is heard. Because the two waves don't perfectly coincide. they don't completely cancel, but they do greatly reduce the acoustic output in the bass. If these two signal were combined electrically, however, complete cancellation would occur. Note that if you reverse the red and black leads on BOTH loudspeakers, there is NO phase shift between the left and right signals, thus no cancellation occurs. Can i have my dinner now?
Direk
