referred to as l u2212 r herein however the r u2212 l may be used is modulated using suppressed carrier amplitude modulation with a carrier frequency 120 of 38 khz a 19 khz reference signal which is referred to as a pilot tone 115 is transmitted as well although not discussed herein there are optional auxiliary data transmission channels such as the subsidiary communications authorization sca channel that are generally transmitted at lower power and higher frequencies e g beyond 53 khz note also that although the currently used pilot tone and carrier frequencies 19 khz and 38 khz respectively are discussed herein the current systems and techniques may be applied for frequencies different than those in current use both the sum and difference signals may be pre emphasized according to the itu specification the l r l u2212 r and the pilot signals form a multiplexed signal that is then frequency modulated to the desired carrier frequency and transmitted at the receiver the 38 khz carrier needs to be recovered using 19 khz pilot reference signal in order to detect the difference signal fig2 shows a functional block diagram of a digital implementation of an fm receiver 200 a radio frequency rf analog front end 210 receives an fm signal from an antenna 220 and transmits an analog signal to an fm channel select filter 230 which filters out the desired program channel an analog to digital converter adc 235 converts the resulting analog signal to a digital signal note that the received analog signal may be converted to a digital signal prior to selecting the desired channel in some implementations the digital signal is demodulated using a digital baseband processor 240 described in more detail below one or more digital to analog converters dacs.