The parameter is from -127 (full left bias) through 0 (centre = normal) to +127 (full right bias). Other values are undefined. For balances <= 0 the left channel is played at full volume and the right channel is attenuated according to the distance from zero. At -127 the right channel is silent. Similarly for balances >=0 the right channel is played at full volume and the left channel is attenuated.
Note that full volume in the previous paragraph is actually the current volume setting.
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