74HC4051 Why have a VEE / Negative supply Connection?

[jwhitmore]

The title might alternatively be "Why did that work?". I wanted to switch my electric guitar about with a uC and decided I'd try the 74HC4051 [1]. So I bread boarded a simple circuit. The chip has both VCC, Gnd and VEE connections, but to keep it simple I connected VEE to Ground just as a simple test, with a single +5V rail. My first test was to just measure resistances between pins and check that I was switching correctly. That worked, so I decided that I'd connect up my signal generator and try to switch a sine wave through the chip. As I've got VEE connected to ground I assumed that it would not fully work, but might as well test that it half works. I expected the sine wave to be cut off when it went negative, but it fully worked, both the positive portion of the sine and the negative?

Maybe I should just accept that it works and I don't need a negative supply rail connected, but obviously I have misunderstood something. I went through the datasheet again [1] but I'm missing something in all the electronic specifications. I'm sure the manufacturer wouldn't add a negative supply pin if it wasn't needed?  So do I need a negative supply rail.? I'm left scratching my head.

[1] https://assets.nexperia.com/documents/data-sheet/74HC_HCT4051.pdf

[MasterT]

Check page 22, distortion. Otherwise it would be o'k on single +5 power, assuming biasing input with 2 resistor (forming 2.5V voltage) and applying signal from SG via Capacitor.

[TimFox]

The "ground" pin is actually an input, being the reference voltage for logic low on the switching input.  The actual switches, level shifter, and switch driver operate between the positive and negative voltages, so that a ground-referenced logic input can switch an analog signal that goes both sides of ground, up to the levels specified in the datasheet.