Dale & Lewis Chapter 3 Data Representation Analog and digital information The real world is continuous and finite, data on computers are finite need.

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Slide 2 Dale & Lewis Chapter 3 Data Representation Slide 3 Analog and digital information The real world is continuous and finite, data on computers are finite need to approximate real-world data for our computational needs Analog data: information represented in a continuous form Digital data: information represented in digital form Slide 4 Noise in signals Slide 5 Digitizing a signal Sample the signal in time within discrete levels The pieces are numbered The binary number system is used to represent the numbers n bits can represent 2 n numbers Q: how many bits are needed to represent m numbers? Actual number of bits that can be easily addressed in a computer sets some constraints Slide 6 Storing sound on media Grooves in a record Analog: a record (45 minutes in an LP) about 10 3 sound levels (depending on wear) Digital: typically up to 24-bit Pits in a CD Slide 7 Sampling & reproducing sound the y axis The higher the number of levels used to sample the y-axis of a waveform, the higher the dynamic range range of sound volume levels The human ear can distinguish a factor of 10 7 in sound levels, but perception in a concert hall is about 10 4 levels CD quality sound is recorded in 16 bits, though producers tend to compromise quality for loudness 4-bit sampling 32-bit 8-bit Slide 8 Sampling & reproducing sound the x axis The higher the frequency of sampling intervals the x-axis of a waveform, the better are high-frequency sounds reproduced The human ear generally distinguish frequencies between 20 Hz (rumble) and 20,000 Hz (mosquito buzz) Sounds are sampled at 44,100,00 Hz to ensure the capture of peaks and valleys in a 20,000 Hz wave allow some flexibility in the electronics to filter out aliasing effects 22.05 kHz 8 kHz Slide 9 Audio formats WAV compressed or not AU begun with 8 kHz sample rates AIFF uncompressed and lossless (10 MB per minute) VQF compressed, marketed as alternative to MP3, but didnt become popular Slide 10 MP3 format MPEG-2 Audio Layer III (Moving Pictures Experts Group) Lossy compression algorithm 128 kb/s deemed a sufficiently faithful reproduction, 1/11 th the size of a CD quality audio file perceptual encoding, loose information where the listener will likely not notice Can contain audio file metadata in a section of the file (ID3 tag) Uncompressed, Vorbis compression, MP3 compression