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Signal Digitization Analog vs Digital Signals

An Analog Signal. 0. 0. 1. 1. 0. 0. 0. 0. 1. 1. 0. 0. 1. 1. 1. 1. 0. 0. 1. 1. A Digital Signal. Signal Digitization Analog vs Digital Signals. What type of signal do we encounter in nature? What type of signal is required by computers?

brett-nolan
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Signal Digitization Analog vs Digital Signals

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  1. An Analog Signal 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 A Digital Signal Signal DigitizationAnalog vs Digital Signals What type of signal do we encounter in nature? What type of signal is required by computers? What are the issues involved in converting from analog to digital?

  2. The amplitude can take on an infinite number of possible values Amplitude To get an exact copy of the signal, an infinite number of samples must be taken. Time Signal DigitizationAnalog Holds a Lot of Information The Analog Signal: A Closer Look Can a computer represent an infinite number of values?

  3. Sampling – breaking a signal up into discrete pieces by measuring the signal at regular time intervals. The higher the sampling rate the better the quality of recording! Signal DigitizationA way to overcome the “time” problem Amplitude Time

  4. 1111 1101 1100 1011 1010 1001 1000 0111 0110 0101 0100 0011 0010 0001 0000 Quantizing – grouping the infinite set of possible values into a finite number of bins and then assigning a binary number to each bin. Signal DigitizationA way to overcome the “value” problem Amplitude Time

  5. 1111 1111 1111 1101 1101 1100 1100 1100 1100 1100 1100 1100 1011 1011 1011 1011 1010 1010 1010 1010 1010 1010 1010 1010 1001 1001 1001 1001 1001 1000 1000 1000 1000 0111 0111 0111 0110 0110 0100 0100 0100 0011 Signal DigitizationVoila! The analog signal is now digital! 0011 0110 1010 1011 1001 1100 1001 1101 1100 0111 …

  6. Storing Audio SignalsWave Files • a digital audio representation • uses a sampling and quantization to store sound 0 4 bytes 'RIFF' 4 4 bytes <file length - 8> 8 4 bytes 'WAVE' 12 4 bytes 'fmt ' 16 4 bytes 0x00000010 // Length of the fmt data (16 bytes) 20 2 bytes 0x0001 // Format tag: 1 = PCM 22 2 bytes <channels> // Channels: 1 = mono, 2 = stereo 24 4 bytes <sample rate> // Samples per second: e.g., 44100 28 4 bytes <bytes/second> // sample rate * block align 32 2 bytes <block align> // channels * bits/sample / 8 34 2 bytes <bits/sample> // 8 or 16 36 4 bytes 'data' 40 4 bytes <length of the data block> 44 bytes <sample data>

  7. Storing Audio SignalsMusical Instrument Digital Interface (MIDI) Files • a description of musical events, NOT a digitization of an audio signal • representation of a sound includes values for the note's pitch, length, and volume • very compact relative to digital audio Delta Time(decimal) Event Code (hex) Other Bytes (decimal) Comment 0 FF 58 04 04 02 24 08 4 bytes: 4/4 time, 24 MIDI clocks/click, 8 32nd notes/24 MIDI clocks 0 FF 51 03 500000 3 bytes: 500,000 usec per quarter-note 0 C0 5 Ch. 1, Program Change 5 96 90 76 32 Ch. 1 Note On E4, piano 0 80 76 64 Ch. 1 Note Off E4, standard 0 FF 2F 00 Track End

  8. Overcoming Limited BandwidthCompression and Streaming • Compression – reducing the amount of space needed to represent video or audio. • Streaming – instead of downloading the whole video or audio, get enough to start playback and then continue download in the background. Which download technique will/won’t work when listening to web radio?

  9. CD Trivia • How many samples per second are taken for a CD? 44,100 (sampling rate of 44.1 khz) • How many bits per sample? 16 (Other factors: error correction, 2 sample streams for stereo)

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