Digital Sound and Remix:Recording

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Contents 1 Outline 1.1 What is sound? 1.2 Analog 1.2.1 Mechanical Recording 1.2.2 Magnetic Recording 1.2.3 Recording on Film 1.3 Digital 1.4 Digital Recording 1.5 Digital Audio 1.6 Microphone and Recording Techniques 1.7 File Formats 2 Terminology 3 External Links

Outline

What is sound?

Sound is vibration, as perceived by the sense of hearing.

The vibrations pass through a medium. If there is no medium (as in space), then there is no sound.

A sound wave is usually represented graphically by a wavy, horizontal line; the upper part of the wave (the crest) indicates a compression and the lower part (the trough) indicates a rarefaction.

Frequency and Wavelength - "The frequency is the number of air pressure oscillations per second at a fixed point occupied by a sound wave. One single oscillatory cycle per second corresponds to 1 Hz. The wavelength is the distance between two successive crests and is the distance that a wave travels in the time of one oscillatory cycle."

Suppose sound is emitted as a sine wave travelling outward spherically from a point source. The pressure (above ambient, see gauge pressure) of the sound wave can be written as

Amplitude - The amplitude is the magnitude of sound pressure change within the wave

Velocity - "Sound's propagation speed depends on the type, temperature and pressure of the medium through which it propagates. Under normal conditions, however, because air is nearly a perfect gas, the speed of sound does not depend on air pressure. In dry air at 20 °C (68 °F) the speed of sound is approximately 343 m/s (approximately 1 meter every 2.9 milliseconds). The speed of sound relates frequency to wavelength. Thus, a tone of 343 Hz (F4 minus 31 cents) traveling in air has a wavelength of 1 meter."

Perception of Sound

Humans can generally hear 20 and 20,000 Hz. "The amplitude range of sound for humans has a lower limit of 0dBSPL, called the threshold of hearing. Sound is technically at its upper limit at 194.09 dB. Above this level it should be called a shock wave. Sounds begin to do damage to ears at 85 dBSPL and sounds above approximately 130 dBSPL (called the threshold of pain) cause pain."

Noises are irregular and disordered vibrations including all possible frequencies. Their picture does not repeat in time. The noise is an aperiodic series of waves.

• Flash animation of how it works

Analog

Mechanical Recording

• 1796 a Swiss watchmaker named Antoine Favre - http://en.wikipedia.org/wiki/Musical_box
• 1857 - Leon Scott invented the 'phonoautograph', the first device to record arbitrary sound in 1857
• 1877 - The phonograph built expanding on the principles of the phonoautograph. Invented by Thomas Edison in 1877, the phonograph was a device with a cylinder covered with a soft material such as tin foil, lead, or wax on which a stylus drew grooves. The depth of the grooves made by the stylus corresponded to change in air pressure created by the original sound.
  • disadvantage of the early phonographs was the difficulty of reproducing the phonograph cylinders in mass production.
• 1877 - This changed with the advent of the gramophone (phonograph in American English), which was patented by Emile Berliner in 1887. - http://en.wikipedia.org/wiki/Gramophone_record
  • Instead of recording by varying the depth of the groove (vertically), as with the phonograph, the vibration of the recording stylus was across the width of the track ( horizontally). The depth of the groove remained constant
  • Early disc recordings and phonograph cylinders had about the same audio fidelity (despite the cylinder's theoretical advantages of constant linear groove speed and greater dynamic range of the hill-and-dale groove geometry). However, disc records were easier and cheaper to mass produce. (like diff. between vhs and beta...all about cheapest duplication)
  • From the beginning, the flat disks were easily mass-produced by a molding process, pressing a master image on a plate of shellac.
  • In 1920's switched to vinyl

Magnetic Recording

• 1898 by Valdemar Poulsen in his telegraphone.
• On Christmas day 1932 the British Broadcasting Corporation first used a tape recorder for their broadcasts.
  • Marconi-Stille recorder, a huge tape machine which used steel razor tape 3mm wide and 0.08mm thick.
• mid-50's magnetic tape (ampex)
  • The typical professional tape recorder of the early 1950s used ¼" wide tape on 10½" reels, with a capacity of 2400 feet (731.5 metres). Typical speeds were initially 15 in/s (38.1 cm/s) yielding 30 minutes' recording time on a 2400 ft (730 m) reel. 30 in/s (76.2 cm/s) was used for the highest quality work.
• Multitrack stereo developed by Germans in 1943
• early 1950s - Much of the credit for the development of multitrack recording goes to guitarist, composer and technician Les Paul
• In a professional setting today, such as a studio, audio engineers may use 24 tracks or more for their recordings, utilizing one or more tracks for each instrument played.
• 1963, Philips introduced the Compact audio cassette,

Recording on Film

• The Jazz Singer used a process called Vitaphone, a process that involved synchronizing the projected film to sound recorded on disk. It essentially amounted to playing a phonograph record, but one that was recorded with the best electronic technology of the time. Audiences used to acoustic phonographs and recordings would, in the theatre, have heard something resembling 1950s "high fidelity."
• Vitaphone was quickly supplanted by technologies which recorded a sound track optically directly onto the side of the strip of motion picture film. This was the dominant technology from the 1930s through the 1960s and is still in use as of 2004.
• There are two primary methods for optical recording on film. Variable density recording uses changes in the darkness of the soundtrack side of the film to represent the soundwave. Variable width recording uses changes in the width of a dark strip to represent the soundwave.
• In both cases light that is sent through the part of the film that corresponds to the soundtrack changes in intensity, proportional to the original sound, and that light is not projected on the screen but converted into an electrical signal by a light sensitive device.
• Now done with digital audio sync'd to the film (syncing tech. is better now)

Digital

Digital Recording

• The first digital audio recorders were reel-to-reel decks introduced by companies such as Denon (1972), Soundstream (1979) and Mitsubishi. They used a digital technology known as PCM recording.
• Alesis and first released in 1991, the ADAT machine is capable of recording 8 tracks of digital audio onto a single S-VHS video cassette. The ADAT machine is still a very common fixture in professional and home studios around the world.
• NOW: Hard disk recording
  • Hard disks are huge! Hard disks are cheap! Computers are powerful! Computers are cheap! Networking is fast! Network is cheap!
  • hard disk recording takes two forms.
    • One is the use of standard desktop or laptop computers, with adapters for encoding audio into two or many tracks of digital audio. These adapters can either be in-the-box soundcards or external devices, either connecting to in-box interface cards or connecting to the computer via USB or Firewire cables.
    • The other common form of hard disk recording uses a dedicated recorder which contains analog-to-digital and digital-to-analog converters as well as one or two removable hard drives for data storage. Such recorders, packing 24 tracks in a few units of rack space, are actually single-purpose computers, which can in turn be connected to standard computers for editing.

[edit]

Digital Audio

• http://en.wikipedia.org/wiki/Digital_audio
• DYNAMIC RANGE: The dynamic range of 16 bit digital audio is therefore approximately 96 dB, whereas the dynamic range of 24 bit digital audio is 144 dB. 8 bit digital audio has a dynamic range of approximately 48 dB.
• SIZE: The amount of data created by digital audio is quite large. 16 bits per sample at 44.1 kHz creates 705600 bits per second (8 bits = 1 byte). Thus for a stereo recording, approximately 10 MB will be generated per minute. 24 bit, 96 kHz digital audio has a bit rate of 2304000 bits per second, or around 33 MB per minute for stereo. Due to this, different forms of audio data compression have recently become more popular.
• How CDs work: http://electronics.howstuffworks.com/cd1.htm

Microphone and Recording Techniques

• http://en.wikipedia.org/wiki/Microphone
• http://members.aol.com/mihartkopf/
• How microphones work and the different types
• Detailed look at different microphones

File Formats

• http://en.wikipedia.org/wiki/List_of_audio_formats

• For our purposes:
  • Uncompressed
    • WAV
    • AIFF
  • Compressed
    • lossy
  • MP3
  • OGG
    • lossless
  • FLAC
  • AAC

Terminology

• Analog / Digital
• Amplitude (wavelength)
• Dynamic Range
• Add more...

External Links

• http://www.archive.org/ - examples
• http://en.wikipedia.org/wiki/Sound_recording
• http://en.wikipedia.org/wiki/Category:Audio_engineering
• http://en.wikipedia.org/wiki/Microphone
• http://en.wikipedia.org/wiki/Sound