1. A method for audio intelligibility enhancement in a computing device, comprising: detecting environment noise by performing a voice activity detection according to a detected audio signal from at least a microphone of the computing device; obtaining noise information according to the detected environment noise and a first audio signal; and outputting a second audio signal by boosting the first audio signal under an adjustable headroom by the computing device according to the noise information and the first audio signal, wherein the adjustable headroom is at a first value when a signal level of the first audio signal is under a threshold level and the adjustable headroom is at a second value less than the first value when the signal level of the first audio signal is over the threshold level, wherein the adjustable headroom is a maximum allowable increase in a gain of the boosting of the first audio signal.