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Analog to-digital conversion
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Analog to-digital conversion

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  • 1. 1 0 1 0 1 0 1 1 1 1 0 1 0 1 1 1 0 0 0 0 1 1 1 0 1 1 0 0 1 0 1 0 1 0 1 0 1 0 0 0 1 1 1 0 1 0 1 0 1 0
    1
    1
    0
    0
    1
    0
    1
    0
    11110101010010
    1
    1
    0
    0
    1
    0
    1
    0
    11110101010010
    Analog-to-Digital Conversion
    1 0 1 1 0 1 0 1 0 1 0 1 1 0 0 0 0 0 0 0 1 1 0 1 0 1 0 1 1 0 1 0 1 1 1 1 1 1 1 0 1 0 1 1 0 1 0 1 0
  • 2. Objectives:
    Aims:
    • Able to recognise and explain the Basic Parameters of sound :
    - Waveform
    - Amplitude
    - Frequency
    • Able to describe ‘Sample Rate’ and ‘Bit Depth’ in Analog-to-Digital Conversion.
    • 3. Start to develop ideas between Analog and Digital recording methods.
    Able to recognize the three constituents of any sound
    (waveform, frequency and amplitude). Describe the process of Analog to Digital Conversion and the importance of ‘Sample Rate and ‘Bit Depth’
  • 4. Basic Parameters of Sound
    • When you hear a sound, what we actually experience are variations in the air pressure around us .
    • 5. When a vibrating object moves through one complete back-and-forth motion (one cycle), the vibration becomes auditory.
    If this is at a frequency that falls within human hearing, we perceive the sound.
    Human hearing is generally between:
    20Hz to 20kHz
    20 cycles a second to 20,000 cycles a second
  • 6. The parameter of any sound can be broken into three main elements:
    Waveform:
    The “shape” of the sound, more accurately the shape of the vibration.
    • Cycles of vibration are not always smooth and continuous (like a Sine-Wave). Typically complex and jagged in shape and structure.
    • 9. This can be because of factors such as:
    • 10. Physical material object is made from
    • 11. Surroundings; i.e. Room acoustics
    • 12. Speed of vibrations
    Each waveform (sound) has a uniquecharacter affected by many aspects.
  • 13. Frequency:
    This is the human measurement of the amount of vibrations of a sound:
    • We measure frequency in ‘cycles per second’ or ‘Hertz (Hz)’
    • 14. So 15,000 cps = 15,000 Hz
    • 15. Multiples of 1,000Hz are often shown as Kilo Hertz (kHz)
    • 16. So 15,000Hz cab be written as 15kHz
  • Amplitude:
    The amplitude or ‘intensity’ of the sound pressure vibrations that reach our ears creates our perception of the loudness of the sound.
    • We measure amplitude in ‘Decibels’ (dB)
    • 17. This is a Logarithmic unit, human DO NOT hear linear manner.
    An increase of 10dB is needed to produce a perceived doubling of loudness.
    Ordinary conversation is around 60dB
    Increasing to 70dB would be need to seem louder.
  • 18.
  • 19. Recording and Play-Back of Analog Audio:
    • A microphone responds to changes in air pressure – the waveforms and amplitude that make a sound.
    • 20. The microphone translates the sound into an electrical output.
    - The continuous electrical signal produced by a microphone is an alternating current with a waveform and amplitude thatdirectly correspond to the original acoustic
    information.
    If this is captured on a traditional media, such as magnetic tape. When played back it is directly translating the electrical waveform.
    Electrical Signal
    Sound-Wave
  • 21. Digital Information:
    = Analog-to-Digital Conversion =
    Any sound before entering into a digital system must be digitized (turned into binary – numerical information).
    This process is called = Analog-to-Digital Conversion =
    (or often called - A/D Conversion)
    Two essential factors affect this process:
    • Sample Rate
    - Bit Depth
  • 22. Sample Rate - Frequency Resolution
    • Sampling is the process of taking ‘Snap Shots’ of sound at various moments in time.
    • 23. Playback in succession, these ‘snap-shots’ of sound approximate the original signal.
    - Like moving images on a film
    • The sample Rate is the frequency with which these digital snapshots are collected.
    • 24. However in order to accumulate to accurate image of the sound there is an important theory to consider...
  • This process is affected by the ‘SamplingTheory’ or ‘NyquistTheorem’
    Each sound cycle MUST be sampled at least TWO times to produce an accurate representation of a frequency.
    Otherwise will produce false tone and course distortion, this is known as ‘Alias Tones’
    So for high frequencies of 20kHz, the sampling must be above 40kHz – 40,000 snapshots a second!
    As shown on a CD the sample rate is 44.1kHz
  • 25.
  • 26. Bit Depth – Amplitude Resolution
    • The relative amplitude (loudness) of a sample is captured through a process called ‘Quantization’.
    • 27. This simply means that each sample is quantified (assigned) to the closest available value.
    • 28. Because at the most basic level a computer is nothing more than a switch - ‘On’ or ‘Off’ - its language called binary...
    ‘1’ or ‘0’
  • 29.
    • A digital system will break down the amplitude into a number of steps - levels of quantization.
    Most common found on today's systems are: 8 bit - (8x8) = 64 bit
    16 bit – (16x16) = 65,536
    24 bit – (24x24) = 16, 777, 216
    Though larger ‘Bit Depth records a better sound, take more memory.
    No matter how good the system still nothing like the real sound. Because it can naturally only behave and register information like a computer.
    16 bit / 44.1kHz
    • 24 bit / 48kHz = 17Mb of hard drive space
    1 min. Occupies 11.4 Mb
  • 30.
  • 31. Recap Madness:
    Basic Parameters of Sound:
    Amplitude =
    - Since sound is a compression wave, its amplitude corresponds to how much the wave is compressed, the height of the wave, measured in decibels (dB).
    Wavelength =
    - Wavelength is the horizontal distance between an exact position on contiguous waves.
    Frequency/Pitch (Musicians) =
    - Frequency is the number of wavelengths per second (and/or defined time period), measured in Hertz (Hz), above has 4 cycles
  • 32. Digital Information:
    = Analog-to-Digital Conversion
    Any sound before entering into a digital system must digitizedturned into binary – numerical information.
    = Analog-to-Digital Conversion =
    (or often called - A/D Conversion)
    Two essential factors affect this process:
    • Sample Rate
    - Bit Depth
  • 33. Sample Rate - Frequency Resolution
    • Sampling is the process of taking ‘Snap Shots’ of sound at various moments in time.
    • 34. This process is affected by the ‘SamplingTheory’ or ‘NyquistTheorem’
    Each sound cycle MUST be sampled at least TWO times to produce an accurate representation of a frequency.
    Bit Depth – Amplitude Resolution
    16 bit / 44.1kHz
    • The relative amplitude (loudness) of a sample is captured through a process called ‘Quantization’.
    • 35. A digital system will break down the amplitude into a number of steps - levels of quantization.
    1 min. Occupies 11.4 Mb