Tutorials and Topics - Peabody Computer Music

Tutorial 22MIDI Control:Panningbecause it does not cause a noticeable dip in intensity when panning from one side to theother.Speaker-to-speaker crossfadeGiven a standard stereo speaker placement—with the two speakers in front of the listenerat equal distances and angles—if an actual sound source (say, a person playing a trumpet)moved in a straight line from one speaker to the other, the sound source would actuallybe closer to the listener when it"s in the middle than it would be when it"s at eitherspeaker. So, to emulate a sound source moving in a straight line from speaker to speaker,we will need to calculate the amplitudes such that the intensity is proportional to thedistance from the listener.LocRdybxaDistance b is shorter than distance aTechnical detail: If we know the angle of the speakers (x and -x), we canuse the cosine function to calculate distance a relative to distance b.Similarly we can use the tangent function to calculate distance c relative tob. The distance between the speakers is thus 2c, and as the MIDI pan valuevaries away from its center value of 64 it can be mapped as an offset (o)from the center ranging from -c to +c. Knowing b and o, we can use thePythagorean theorem to obtain the distance (d) of the source from thelistener, and we can use the arctangent function to find its angle (y).Armed with all of this information, we can finally calculate the gain for thetwo channels as a . cos(y±x)/d.• Choose “Speaker-to-Speaker Crossfade” from the umenu. Listen to the sound whilepanning it slowly from one channel to the other. You can try different speaker anglesby changing the value in the “Speaker Angle” number box. Choose a speaker angle bestsuited to your actual speaker positions.This effect becomes more pronounced as the speaker angle increases. It is most effectivewith “normal” speaker angles ranging from about 30˚ up to 45˚, or even up to 60˚. Below30˚ the effect is too slight to be very useful, and above about 60˚ it"s too extreme to berealistic.183