Definition and calculation of distortion in grounded emitter amplifier
[edited, added Explicit predictions of Distortion for base AC voltages.]

Willy Sansen and Barry Gilbert have various papers discussing the distortion of bipolar transistors.

The 2nd order and 3rd order distortion intercept points for a bipolar are not the same value, but both are about -14dBv. 

And -14dBv is about 0.2 volts on the base.

The Intercept Point is where the Distortion is the same strength as the Fundamental.

You want to operate far below that point, so the music is enjoyable.

Instead of 0.2 volts, I'd plan on 0.002 volts (2 milliVolts) to be your low-distortion maximum-input amplitude PeakPeak.

If you add an emitter-degeneration resistor that has about 0.25 volts across it DC and AC (no bypass cap), then your distortion drops to 0.1%, from what I recall.

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Predicting distortion levels, using the Intercept Points (IP2 and IP3):

The number I gave (-14dBv) is INPUT intercept Point (input being at the BASE of the transistor). Again, that is an approximate number, and depends on doping profiles (the "N" in the diode equation).

Lets make some predictions.

For IP2, the distortion drops 20dB (10:1) for each 20dB you reduce the input voltage below that 0.2volts (the -14dBv).

Means what? for -60dB 2nd order distortion, you need to make the input be 60dB weaker than 0.2 volts. Or about 200 microVolts.

For IP3, the distortion drops 40dB (100:1) for each 20dB you reduce the input
voltage below that 0.2volts (the -14dBv).

Means what? for -60dB 3rd order distortion, you need to make the input be only 30dB weaker than 0.2 volts, or about 6 milliVolts.

Why is this? you should examine the polynomials, draw some 1:1 input power, a 2:1 output power of 2rd order, and a 3:1 output power of 3rd order.

I've provided a diagram of this, in prior answers.