موضوع: Compression lerning

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  1. #1

    Compression lerning

    Audio Compression: Audio Compression Tutorial
    Made Easy By Amr Total

    Using a compressor on a microphone or on a
    recorded track may seem to be a simple task,
    however, there’s a lot to learn about the theory
    of compression. Understanding this theory and
    why compression is useful will help you in using
    these devices more effectively. Compressors are
    “dynamic range processors” or “variable gain
    amplifiers” (VGA’s). They affect the dynamic
    range of sound by varying the “gain” (volume) of
    that sound.

    If the dynamic range of music is potentially
    near 120db (that’s loud!) and the dynamic range
    of recording devices and live sound systems are
    only near 75-90db, we need a way to control the
    dynamic range so that those loud levels do not
    cause distortion. The dynamic range has to be
    gain reduced to a level appropriate for
    recording or a live concert. This "gain
    reduction" could be accomplished by manually
    riding the fader up and down but our hands are
    not fast enough. A compressor automatically
    controls the volume of a sound, leaving our
    hands free for other things.
    Compressors are used on vocals, bass, guitar,
    drums and almost anything that fluctuates
    widely. Very simply put, a compressor is an
    amplifier whose gain decreases as the input
    increases. It makes big changes into smaller
    changes.
    Most compressors have 4 main controls: input
    level, output level, threshold and ratio. Some
    compressors also have attack time and release
    time controls.
    Input level: is exactly that, the amount of
    input level. When you set it to "O", you get the
    exact level that you are sending from your mic
    pre-amp or from an already recorded track.
    Output level: the amount of output after
    compression.
    Threshold: A set point at which the compressor
    begins to work. Incoming levels below your set
    threshold are unprocessed. Incoming levels above
    your set threshold are compressed according to
    the compression ratio. The threshold on a
    compressor is similar to an air conditioner
    thermostat. When the temperature exceeds a
    certain threshold, the air conditioner kicks in.
    When the temperature drops below threshold, the
    air conditioner shuts off. This is the same idea
    for the threshold of a compressor.
    Ratio: is the ratio of the input signal to the
    output signal after compression.
    Example: 4:1 ratio means if the input is 12db,
    the output level is only 3db. So level input
    (12db) divided by ratio (4) is the output level.
    A ratio of 2:1 would give a 12 db input an
    output level of 6 db and a ratio of 8:1 would
    give an output level of 1.5db. So the rule of
    thumb is, the higher the ratio, the more extreme
    the compression is going to be. Therefore,
    ratios from 2:1 up through 6:1 are considered
    “gentle” and ratios above 6:1 are considered
    “hard”. “Hard” compressing is called “limiting”.
    A limiter is merely a compressor with a very
    high ratio, very fast attack times, fast to
    medium release times and high thresholds.
    Limiters are great for live sound systems as a
    safety device when very high levels are
    introduced into the system. Any signal above the
    threshold is "clipped" off. They protect
    speakers from blowing. 8:1,10:1, 20:1, 100:1 are
    common limiting ratios.
    Attack time: The speed with which the device
    affects the signal. The time it takes to react
    to a signal above the threshold.
    Release time: The rate at which the device lets
    the signal decay. The time the compressor takes
    to return the signal to normal (the way it was
    before hitting the threshold).
    Stereo compressors come in one box with 2
    channels and can be used in 2 different ways.
    You can put 2 individual mics or tracks into it
    and each channel will have completely
    independent settings from each other. Obviously,
    a mono compressor just has one channel. The
    second way to use a stereo compressor is to put
    an entire stereo studio mix or the stereo output
    of a live soundboard into it. This is called
    using the compressor as a Left/Right Stereo Bus
    compressor. When you use it as a L/R Stereo Bus
    compressor, you have to link both sides
    electronically so the same amount of compression
    happens on both sides at the same time.
    A “Frequency Selective Compressor “(De-esser) is
    a special compressor that reduces the level of a
    very narrow band of frequencies. It’s very
    useful when a singer has a strong, sharp,
    sibilant “S” to their voice. Typically in the
    5-8k range. When 5-8k exceeds the threshold, it
    reduces strong, sibilant "S's" without affecting
    the rest of the word.
    There are 2 types of compressors: Tube and solid
    state. They have a wide range of quality and
    price ($200-$4000). Upper mid price and
    expensive compressors can compress a signal
    heavily and you can hardly tell it's working.
    The sound remains much more natural than when an
    inexpensive compressor is compressing.
    Tube compressors have such a great sound that
    sometimes a signal is put through it just to get
    the sound of the tubes while hardly compressing
    it at all.
    Be careful not to overuse a compressor. When
    overused, it creates a very unnatural sound. The
    trick is to learn to use a compressor in a
    subtle manner.


  2. #2
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    مع الشكر

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