A communications device is configured to control the intelligibility of speech in a downlink voice signal during a call. The device determines a current noise level based on sampling ambient acoustic noise and based on a previously determined noise level. The device then determines an overall output gain and a frequency response based on the current noise level and based on a user-selected volume setting of the device. The device modifies the downlink voice signal during the call in accordance with the determined overall output gain and the determined frequency response. Other embodiments are also described and claimed.