non trivial stereo to mono analog circuit

research

http://www.instructables.com/answers/Connecting-left-and-right-audio-channels-together/

$ 1 0.000015625 8.281975887399955 50 5 50
r 608 208 608 272 0 600
r 608 272 608 336 0 600
r 608 336 608 400 0 600
w 608 208 464 208 0
w 608 400 528 400 0
w 608 400 768 400 0
w 608 208 768 208 0
w 464 288 528 288 0
w 464 320 560 320 0
w 608 336 576 336 0
w 528 304 528 288 0
w 560 320 560 272 0
w 560 272 608 272 0
O 768 208 768 176 0
v 464 288 464 208 0 1 800 5 0 0 0.5
v 464 400 464 320 0 1 400 5 0 1.5707963267948966 0.5
w 576 336 576 304 0
w 576 304 528 304 0
403 272 208 400 272 0 14_64_0_4098_10_0.025_1_2_14_3
403 272 320 400 384 0 15_64_0_4098_10_0.025_0_2_15_3
211 768 208 832 208 0 1 8000 1
g 768 400 768 432 0
x 799 254 862 257 4 24 fill\sbar
x 798 287 895 290 4 24 then\splay
s 464 400 528 400 0 1 false
x 456 434 583 437 4 24 make\smusic
o 13 64 0 4098 10 0.1 0 1

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