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The VU meter

Discussion in 'Recording' started by Renegade, May 25, 2003.

  1. Renegade

    Renegade Guest

    I have just begun my venture into the recording world and have many questions without answers. First and foremost could someone explain the reasoning behind the VU meter that reads in negative decibels? I understand the concept of decibels as being a logarithmic scale to simplify the hearing process but why use a negative scale in recording . . . am I missing something? Thank you for your help.

  2. vinniesrs

    vinniesrs Active Member

    May 12, 2003
    Every peice of equipment has a certain dynamic range. From the quietest volume to the loudest. If you look on a channel fader, at the bottom you will see -infinity. That means off. Vu meters usually show you from about -20 to plus 3 or 6. Over the plus 3 or 6, your signal will distort, under -20 your signal is too weak.
    In digital, zero is the point of distortion or clipping.
    Here's the point. Every peice of equipment has self noise. Put all of them together in the signal chain and you get what's called a noise floor. You need to make the level of your recording higher than this by quite a bit, in order to "bury" this noise. This was the real reason a compressor was invented. Originally called the leveling amplifier. Look it up, good info.
    Anyway, if you are recording tracks to tape, try to stay as close to zero as you can without clipping. Plus 3 is okay, plus six is dangerous, and when you saturate a tape with a hot signal the sound changes a bit too.(I kind of like it.)
    Now if you record with digital stuff, the noise floor is much lower, and you can record at -5 -10 or -15db without fear of noise probs.
    If you have adats, record lower than you think you should by 5-10 db, the level meters on these guys lie and tell you they are lower than they really are.(try-20 to -15 on an adat)

    Hope this info helps.
  3. Renegade

    Renegade Guest

    That explains things a little, yet I still don't understand the negaitve aspect and how that translates back into real decibels and the over all volume.

    I'm using digital recording equipment, specifically a Roland VS 2480 which is phenomenal I'm told when you know how to work it. The thing is that I am a songwriter and that's my strongsuit. I feel a bit out of place on this forum for I am only 19 and have no experience whatsoever with recording. I have all these great songs to record but wanna do it right and only once. I've bought decent mics and have really good equipment but as far as mic placment goes and room acoustics I'm lost. Anything you could tell would help I'm sure.
  4. vinniesrs

    vinniesrs Active Member

    May 12, 2003
    The simplest thing for you to do is to set your mic gain(input sens on the roland)by soundchecking the item to be recorded and turning it up until you see a clip(red light on the channel). Once you see this, back off a little bit. Next listen to your sound, and change the placement of the mic if you dont like it. Re-check to make sure that your signal isn't clipping, and then check the level on your track. Your track level(vu meter) should read -10 to -15db. Dont go any higher than this. You do not need to as this is way above the level of the noise in the machine. If you do things this way you will have a clean sound recorded. All of the signal processing features will take lots of practice and there is no way to explain how to use them in general. With specific examples you will find much help there.

    As for the acoustic issues, you will nee to do something. See the acoustics section of this site for info. Very helpful.

    With respect to the volume I will try to explain.
    In theory, 0db on the fader is "unity gain" This means that you are not amplifying the signal any, but you are not subtracting amplitude from it either. You don't really want to amplify it any more than you have to, because then you are probably amplifying noise too. If your fader is at zero and it reads too high on the meter, than pulling it down reduces the volume.(in this case the sensitivity of the mic might need to be decreased by turning it down, or moving it away from the source.)
    If you have to push the fader way up to get the signal within range, then you may need to increase the input sensitivity(mic gain rim), move the mic closer to the source, or increase the volume of the source.(only if it is really quiet.)
    With your workstation, the bottom of the meter represents the smallest amount of sound that will register. The top displays the maximum.

    Also if you tell us what kind of mics you bought we can tell you good ways to use them.

  5. Good Texan

    Good Texan Guest

    Let me preface this post by saying that I'm "pretty sure" this is the case. I hope others here can corroborate my statements. Okay, that being said-here goes:
    The reason the meter has negative numbers is because the dB scale is a measure of the difference between two signals. One measurement would be the difference between a reference pressure/voltage/power(watts) and an input. Another would be between two arbitrary signals. For example, If your meter reads 0dB, that means that the signal you are putting "to tape" is the same level as a predetermined reference level set in your machine(which can be changed during alignment). If it reads +3dB, that means that your signal is 3dB higher than that refernce level. Therefore, a negative reading indicates that your signal is lower than that reference.

    dB=Xlog (input signal/reference)
    dB=Xlog (signal 1/signal2)

    X can be either 10 or 20 depending on what you're measuring. If you're measuring watts or volts, I think it's 10. If you're measuring pressure, it's 20. When you measure pressure, it contains the exponent 2. In algebra, you pull that 2 out in front of the log. That 2 is multiplied by 10 already in front. That's where the 20 comes from.

    I hope this helps.

  6. Renegade

    Renegade Guest

    For my mics I have 4 sm57's, a beta 58, a beta 91, 2 AKG D 2000 E's, and an AT 4033 SE. I am really satisfied with The Audio Technica mic when I comes to vocals. It has a superb sound quality for a relatively low price (600 Canadian). I know I can achieve a decent quality with these mics given the right direction . . . yet equipment is only half the battle and the rest is up to skill.

    One question I have is the newest song I am working on has been recorded with good levels, nothing peaking regularly (just the ocasional peak on the bass drum or tom) yet on the master VU meter it clips in places. I am sending signals through an Aux bus for a loop chorus effect yet its meter reads well also. What am I doing wrong?

    P.S. This sight is phenomenal and those who have responded are an amazing help.
  7. Kurt Foster

    Kurt Foster Distinguished Member

    Jul 2, 2002
    77 Sunset Lane.
    It is just the sum of all the channels making the 2-bus peak. Try muteing different channels until you find the one(s) that is/are causing the peaks. Bring them back a bit and that should be it. you may also try a little (and I mean little) bit of limiting on the 2-bus to prevent the peaking.. remeber, your channel fader gernerally should not be higher than your 2-bus fader.

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