... But why use a Hex CMOS instead of a dual CMOS? ...
from "Electronic Projects for Musicians", Craig Anderton, 1980
"IC1 is a 4049 hex CMOS inverter/buffer that was never really intended for
audio use. It's a
digital IC (the type used in computers), and is generally
grouped with lots of other digital ICs to implement some type of digital
function (microcomputer, industrial control, and so on). But as it so happens,
each inverter of the IC may be modified to run as a
linear (audio) IC,
and because these inverters are based on FET circuitry, distorting them
gives a tube-type distortion sound."
The 4049 is so inexpensive that it was probably never manufactured with less than 6 inverters.
The chip designers had 14 pins to play with. 6 inverters + 2 power = 14 pins.
It's still an extremely inexpensive chip. Mouser will sell them to you for $0.141/chip
( 2,275 minimum )
joke of the day: don't ask me how I know the minimum price.
( does anyone want to buy 2,273 CD4049 chips? I ordered extras

)
bonus joke:
they shipped them to me in packs of 8.
I'm thinking of opening up a retail store:
CD4049s 'R' usopen mon-fri - noon to 8:00pm
closed on weekends and holidays for inventory control