Funnily enough this came up on the developer’s mailing list just the other day.
How panning works in Audacity:
Panning, whether mono or stereo is on a scale of +/- 1.0 where 0.0 is centre panned,
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Stereo tracks:
Pan at zero plays both left and right channels without modification (“unity gain”)
Panning to the right (positive value of pan) keeps the right channel unmodified, and reduces the left channel proportionally to the amount of pan. When panned all the way to the right, the left channel is silent.
Panning to the left (negative value of pan) keeps the left channel unmodified and reduces the right channel proportionally to the amount of pan. When panned all the way to the left, the right channel is silent. -
Mono tracks:
Basically the same as for stereo track, though it’s (obviously) the one mono track that plays through left and right. The level in left and right channels follows the same rules as described above.