Fairly soon after the introduction of talkies in the late 1920s, the movie industry settled on using an analogue optical soundtrack on the edge of the film to carry the sound. This was read by the projector and converted to an electrical audio signal. This was a very noisy medium, so in the absence of advanced noise reduction technology such as Dolby A (the cinema equivalent of, and precursor to, the Dolby B and C noise reduction systems on compact cassettes), the situation was eased by sharply cutting the treble response (at around 5kHz). The bass was also cut, which accounts for the characteristic pinched sound of old movies. The recommended system of frequency response tailoring was called 'Academy Sound'.