A method and apparatus provides for encoding an audio signal. A bit rate value is received. A set of energy thresholds based on the bit rate value is selected. The set of energy thresholds is one of a plurality of sets of energy thresholds. The energy thresholds of each set of energy thresholds correspond on a one-to-one basis with a set of sub-bands of the audio signal. The audio signal is received. The energy of each sub-band of the set of sub-bands is determined. A highest frequency sub-band that has an energy exceeding the corresponding threshold is determined. A selected bandwidth of the audio signal is encoded. The selected bandwidth includes only those frequencies of the audio signal that are in the highest frequency sub-band that has an energy exceeding the corresponding threshold, as well as the lower frequencies of the audio signal that are above a high-pass cut-off frequency.