why do we use compressors?

Discussion in 'Recording/Live Sound' started by Guitarplayerdan, Oct 22, 2008.

  1. Guitarplayerdan

    Guitarplayerdan Member

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    Im still relatively new to recording.

    I understand what compressors do, but how do this really make our audio source sound better. Why do I want a threshold on my audio. How does it make our recordings "perfessional". I watched tons of demos with compression off and then on, and EVERY time i couldn't hear a difference.

    Do I want a compressor so I can recieve a more consistant level from the audio source and not a level that jumps from to quite to peaking?
    I understand why I would want this live but why in the studio?

    Someone also told me that comprssor brings up your quite spots and brings down you louder spots, how does it bring up I thought it only brought down?
     
  2. alvagoldbook

    alvagoldbook Member

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    Compressors ultimately make mixing easier.

    For instance, a distorted guitar is typically very compressed. The amp compresses the signal. It levels out the loud notes from the soft notes and make them fairly uniform. For that reason, mixing in the proper level of distorted guitar is pretty easy. You generally won't have a part that is louder than another part.

    Now take vocals. Unlike guitars, bass, drums, keyboards, etc, vocals are not mechanical. They are always imperfect. For that reason some syllabels or words will be louder than others. It makes no sense to mix a vocal for every word. Instead you compress it so that the loudest words are at the same general level as the softest words.

    Bass, or any clean tone, always have issues with this, and compression becomes very important. The amount of compression used is important too. Tons of compression can make something sound life-less or artificial. You might actually want that (it's useful in metal) or you might want less.

    Some compressors color the sound more than others. Usually very weak compressors don't color the sound as much as more powerful ones. Keep in mind a powerful compressor isn't necessarily a better one.

    A lot of pros when mastering send the entire mix through a compressor (usually a tube outboard compressor) in order to raise up the levels to CD-listening volumes, but it also makes everything just sound warmer and professional.

    It takes a while to develop an ear for recording, mixing, and mastering. Just like it took a while to develop an ear to tune your instrument. It took me about two years. I listen to stuff I mixed a while back, and it's pretty embarrassing now. Just keep working at it and training your ears.
     
  3. Jan Folkson

    Jan Folkson Member

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    First off, a compressor won't make your recordings "professional" any more than any other piece of gear would. They essentially make a sound source LESS dynamic, meaning a smaller difference between the loudest and softest spots.

    A compressor works by attenuating the loud spots based on a threshold that you set (in some compressors it's set by the input level or ratio setting) thereby allowing you to make the whole signal louder, via the output gain control, without fear of clipping. Essentially making the quiet spots louder.

    In the hands of a skilled engineer they can be used to emphasize the attack portion of a sound source thereby adding more 'punch' to a recording. In the hands of an unskilled user it can impart a smallness or dull sound along with other unpleasantries like pumping etc.
     
  4. drewl

    drewl Member

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    as good as my one bass player is, when recording his volume would jump around alot due to his bass and his fingering.

    I tried to get him to use a pick or set the pickups on his bass to no avail so I had to compress the shite out of him to get a good even signal.
     
  5. drfrankencopter

    drfrankencopter Member

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    The other responses have the details covered, but in a nutshell it's the following reasons:
    1) To even out volume changes (e.g. dynamic range control, as it would typically be done on a vocal track, or full mix)
    2) To limit rapid transients (spikes, string slap, etc)
    3) To shape the transient response of an instrument (e.g. grafting a 'crack' onto a snare)
    4) To add sustain (e.g. on a room mic to make the reverb time appear longer)
    5) To increase apparent loudness by reducing the peak to average level ratio

    Cheers

    Kris
     
  6. fr8_trane

    fr8_trane Member

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    I agree with the above but would combine a couple of those and add 1 more for a smaller more generalized list

    1. Limit Dynamic range - The includes clipping peaks and raising average level. The threshold and ratio are the key parameters here

    2. Wave shaping. Increasing or decreasing attack and sustain. Attack and release settings are crucial here

    3. Color. Difficult to explain with words but analog compressors like the 1176 and LA-2A can add a color to the signal just by being in line (no actual compression going on). Furthermore by using compressors in ways they were not designed to do (the all-in setting on an 1176 for example) you can create radical yet musically useful sounds. This depends on things like a tube signal path, input and/or output transformers, and harmonic distortion.
     
  7. Guitarplayerdan

    Guitarplayerdan Member

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    thanks kinda what i thought I just wanted to know for sure.
     
  8. kludge

    kludge The droid you're looking for

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    Here's an example... the other day, I was recording a vocalist. He was afraid he was "swallowing" the first word in each line of a particular verse. Turns out it was just a dynamics issue - the first syllable was coming out too softly relative to the rest. I made a copy of his vocal and compressed the copy rather strongly, then mixed that back in with the regular vocal. Now the first syllables are clearly audible, but the overall dynamic feel of the vocal is preserved. (that technique is called "parallel compression, btw)

    In a less pleasant way, compressors are now used for the "loudness wars". Ever notice how one song can seem louder than another, even if the peaks are the same? That's because one song is more compressed than another, so there's less dynamic range. It brings the average level up. Of course, it also makes the music less dynamically interesting. That's one reason modern rock and pop sucks.
     
  9. Gtr_Eng

    Gtr_Eng Member

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    Improves the signal-to-noise ratio during recording. Very important in the old days of tape based recordings. Pretty much everything else mentioned in this thread is a byproduct of this, ie. during the process of recording highly dynamic sources they found that compression made things sound better if done properly. The use of compression has evolved from this simple idea over the years.

    Nowadays, as people have already mentioned, compression is used to control dynamics as well as sculpt the sound. Different compressors have different tonal characteristics and can be used just like reverbs and other effects are used. Compression has the effect of bringing a vocal or other instrument more forward in the mix. Conversely, reverb tends to move things back in the mix. A good mix will utilize all dimensions of the sound field. These being left, right, near, far, top, and bottom. Compression is a valuable tool for manipulating the sound field as well as controlling dynamics and imparting pleasing tonal characteristics.

    Too much compression will also cause things to sound small. More highly dynamic sounds will tend to sound larger.

    A pushed tube guitar amp is essentially a big tube compressor.
     
  10. drfrankencopter

    drfrankencopter Member

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    No, compression alone reduces S/N by reducing the peak signals, and bringing up the noise floor. But, compression compression and expansion was used for improving S/N (in the form of dBX).

    Compressors were probably originally introduced to the audio word for AM radio transmission, and to control record cutting lathes.

    Cheers

    Kris
     
  11. Gtr_Eng

    Gtr_Eng Member

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    Yes and No. Compression alone does reduce signal to noise ratio with respect to a given signal as it is going to tape. However, I'm talking about the signal to noise ratio relating to tape noise. The use of compression allowed for a hotter signal to tape which improved the S/N ratio for subsequent processing.

    You are talking about noise inherent in the recording chain prior to printing to tape. The noise from high quality mic/preamp/cable are minimal compared to the noise generated in tape based recording. What you lose in S/N at this stage is relatively inconsequential when compared to the gains achieved by recording a hotter signal in the first place.

    Todd
     
  12. gainiac

    gainiac Senior Member

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    Because their is only so much bandwidth for a given medium, therefore to fit your program material you need to squeeeze it down to size in a relative fashion.
     
  13. fr8_trane

    fr8_trane Member

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    Gotta disagree here. If you are recording a clean guitar thru a tube amp, compression will make the background amp hiss louder regardless of medium. Listen to some old steve miller songs like jet airliner - his breaths are as loud as the actual vocals- a clear sign of heavy compression and reduced signal to noise.

    Increasing the s/n ratio of tracks recorded to tape is as simple as sending a hotter signal (no compression necessary). Of course when you hit tape with more signal than it can handle you get tape saturation which is a form of compression itself - and a very nice sounding one at that.
     
  14. Jan Folkson

    Jan Folkson Member

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    Not sure I understand where you're coming from gainiac...


    We're discussing audio compression not data compression.
     
  15. Jan Folkson

    Jan Folkson Member

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    I see where you're coming from gtr, but as a rule compression lowers the s/n ratio by bringing up the noise floor in the recording. What you're saying is: In effect, recording a hotter signal increases the the signal relative to the mechanical noise inherent in tape machines and by incorporating a limiter you can get a hotter signal to tape... Which isn't wrong btw.
     
  16. buddyboy

    buddyboy Gold Supporting Member

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    All I know is I used to love how they would compress that hell out of Stephen Stills' electrics and acoustics during his time with the Buffalo Springfield. Made everything sound huge, particularly his acoustics.
     
  17. Gtr_Eng

    Gtr_Eng Member

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    Nothing you said disagree's with what I said. I said the noise inherent in a mic/preamp/cable. You're talking about the noise inherent in a source. Obviously if you take a noisy signal and boost it's level while decreasing the headroom you'll get a noisier signal.

    As far as your second paragraph, tape saturation(as you pointed out) is a particular type of compression. It's a particular type of compression that has a particular type of sound. This is entirely consistent with everything I've said. Boosting the signal to the point of tape saturation will also boost the noise from the guitar amp for that matter. So I don't really understand your point as it relates to mine.

    Listen to Jethro Tull if you really want to hear some odd sounding breathes. They are all over his flute solo's and once you recognize them you can barely listen to it without laughing.
     
  18. drfrankencopter

    drfrankencopter Member

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    Compression does not improve S/N...period. By definition it reduces S/N by raising the volume of the noise floor relative to the peak signal.

    BUT....compression can be used to take a wide dynamic range signal, and record it on a dynamic range limited medium (like an old tape machine). Yes, S/N is the reason why the dynamic range of the tape machine is limited, but using a compressor does not improve on this figure...it just lets you make use of the limited range you've got. (PS: I spent years recording on a 2" tape deck with 60dB dynamic range....I never felt dynamic range limited...but then again I recorded rock with meters well into the red).

    The only way compressors can help with S/N is if you compress the signal, store it on tape, and then expand the result. This is the way dbx and Hush (and maybe even some Dolby variants) improve the S/N of analog tape machines.

    Cheers

    Kris
     
  19. Gtr_Eng

    Gtr_Eng Member

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    Yes:)

    Looking back at my first post I realize I didn't really explain myself well. I was trying to make the point that in the old days they started using compression simply to get a better level to tape and thereby minimize the tape noise. They then came to realize that compression itself made some things sound better. It was through this evolutionary process that we have gotten to the point we are at now where compression is used all over the place for a variety of reasons. I probably shouldn't have started out with a blanket statement about signal to noise ratio without explaining which signal and noise I was specifically talking about. I was just trying to help the OP by giving a little backstory. Unfortunately I mostly just confused everyone about what I was trying to say.:confused:

    Todd
     
  20. gainiac

    gainiac Senior Member

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    What Dr. Frankenkopter talks about is what I'm referring too.......Analog mediums have a bandwidth limitation too.

     

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