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Topic: What does a compressor do?

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  1. #1

    What does a compressor do?

    What does compression do to a wavefile and samples?

    These sequences for trumpets are the same, but one sequence has a compressor insert for each of the trumpets (Bb trumpet and C trumpet) while the other does not have any compression.

    Fandango


    Fandango B


    Which sequence sounds better?

    I think I favor the compressed signal, but what does the compressor actually do? It's more than loudness. So what am I hearing?

    Will this have a similar effect on woodwinds and strings?

    I'd like to know your view on this.

    Marko

  2. #2

    Re: What does a compressor do?

    http://en.wikipedia.org/wiki/Dynamic_range_compression

    A compressor basically reduces the dynamic range of the file by reducing the level of higher level sounds.

    A limiter is a type of compressor in that any sound above a threshold level is reduced to that level, the compressor reduces the level of sounds exceeding a threshold by a fixed amount.

    For example - (sum maths I'm afraid)
    threshold set at -6db with a compression ratio of 1:2
    Any sound below -6 db is unaltered, whilst those above are reduced
    A sound at -4db exceeds the threshold by 2db, with a ratio of 2:1 then 1db (2 / 2) is subtracted from the -4db sound leaving a sound of -5db

    threshold set at -6db with a compression ratio of 1:8
    This time the reduction factor is to 2db / 8 = 1/4 db, that is the sound passes through but reduced from -4db to -5.75 db

    Compressors are used a lot by broadcastors of light music as they prevent very loud sections of music from sounding very loud on receivers. The broadcast level remains very close for all music.

    If your DAW has a compressor built in try a running a sound with a loud transient thru it and check the wave shape before and after.

    Any uncompressed sound should sound better, but compression is a tool to help cover up errors.

    Hope this is some help
    Derek
    Things may come and things may go but the art school dance goes on forever
    NOW WITH Cubase 5, JABB,GPO, Fender Strat, Ibanez RG, Yamaha Fretless Bass, Framus Archtop, The Trumpet and Mr T Sax, together with GREEN SEALING WAX


  3. #3

    Re: What does a compressor do?

    Thanks Derek.

    I will mull that over for a while.

    Marko

  4. #4

    Re: What does a compressor do?

    Compression is largely about loudness, as Derek has detailed.

    I prefer the sound of the first of your two samples, which I think is uncompressed - there seems much more "space" around the two trumpets, whereas the second sounds little muffled and tight in comparison. My volume meter shows that the second sample has a peak volume of 5dB less than the first.

    A common key aspect of using a compressor, particularly in pop and rock music, is that the peak volume level after compression is brought back to the original level, so that in effect the compressor has then acted to bring the lower volumes up closer to the peak of he louder volumes, making it seem louder overall.

    With real instruments though, particularly in acoustic/classical approaches, care has to be take because the volume reduction ratio is applied equally across all overtone frequencies in each note's sound sprectrum, which can then alter the overall balance (or EQ) of those frequencies and change the sound of the instrument, so EQ is usually applied after compression to restore the original balance. It may be in your example that we hear proportionally less of the quieter bright/high frequency overtones of the trumpets, giving a slightly duller sound.

    Whether the compressed is better or not depends entirely on what sound you want to achieve.

  5. #5

    Re: What does a compressor do?

    Thank you for the explanation Peter.

    I prefer the first to the second, but it's the first one that is compressed.

    Now I am wondering how much I should use this on my other mixes. Will it sound as good on strings, for example as it does with the brass?

    I'll experiment of course.

    Thanks again for the account.

    Marko

  6. #6

    Re: What does a compressor do?

    Hey Marko,

    Can you tell us what compressor you used on the above example? Was it a plug-in or hardware etc.

    Thanks.

  7. #7

    Re: What does a compressor do?

    MODE,

    The compressor is a plug-in from Vienna Suite (for Vienna Instruments). I used the basic compression preset for each instrument. I think I used the same preset for each trumpet and did not tweak anything.

    Is that specific enough?

    Marko

  8. #8

    Re: What does a compressor do?

    Quote Originally Posted by Marko View Post
    MODE,

    The compressor is a plug-in from Vienna Suite (for Vienna Instruments). I used the basic compression preset for each instrument. I think I used the same preset for each trumpet and did not tweak anything.

    Is that specific enough?

    Marko
    Yup! That's what I wanted to know. Thanks.
    BTW: The first recording definitely sounds better to my ears as well.

    - Gavin

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