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Electrical and Computer Engineering
ECE 198

Your NamenetidGroupNamenetidNamenetidNamenetid ECE 198 Worksheet 7 Digital cell phone calls In 2007 the FCC stopped requiring cell phone carriers to support analog cell phone calls While the cell phone carriers trumpeted this change as a critical revolution in the quality of cell phone calls Higher clarity Crisper sound the hidden reality is that digital cell phone calls cost a fraction to transmit All human speech is produced from a small set of basic sounds These base sounds are composed of a set of samples By performing arithmetic operations on these base sounds we can synthesize any human voice Consequently we can reproduce any voice call with a set of base sounds a codebook and arithmetic operations filters Rather than transmit a recording of your voice the analog method digital calls transmit data indicating which base sounds to use and control data for the filter In this worksheet we will explore a simplified version of this system 1 The codebook for the base sounds of a human voice and the filter operations must be the same across all digital cell phonesWhy Without the same codebooks and filters the data could not be interpreted 2 Creating the codebook Because the codebook is the same for all cell phones we can use a ROM to store the codebook If there are 128 base sounds and each base sound is encoded with 16384 bits 1024 samples of 16bit audio what size ROM would we need to create the base sounds 27 x 16384 ROM 3 Creating the filters Similarly because the filter operations are the same for all cell phones we can use an additional ROM and an arithmetic logic unit to build our processing unit The arithmetic logic unit will combine the data from the codebook with the data in the filter ROM When we combine the data we synthesize the human voice Suppose that we need 64 filters that are each composed of 16384 bits what size ROM would we need to store the filter data 26 x 16384 ROM 1
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