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dB readouts on Analog + Digital

Discussion in 'Recording' started by EIK, Jun 6, 2003.

  1. EIK

    EIK Guest

    I'm seeing a big difference in dB levels when comparing my analog mixer to my digital read out in my Echo Layla24 Console.


    -PS This message was erased (while Kurt was posting a reply I take it) earlier on because I found out what was going on. I wasn't a 100% sure why it was happening though.
     
  2. Kurt Foster

    Kurt Foster Distinguished Member

    You don't say what kind of mixers you are using but I would venture a guess that you are seeing the difference of digital scale vs. analog VU scale. 0 VU is equivalent to -16dB digital. Kurt
     
  3. EIK

    EIK Guest

    Oops, I edited that, probably while you were posting. I'll go back and briefly fill in others.

    I have a Mackie SR?32 VLZ Pro for input and a 1202 VLZ for monitoring.

    What you're saying about digital vs. analog totally makes sense in this situation.

    So I guess that means I should run my analog inputs close to +20 dB, since that will be a "hot" signal close to 0dB in the digital realm? I grew up with analog ..

    Thanks Kurt.
     
  4. Kurt Foster

    Kurt Foster Distinguished Member

    No not that hot. In digital land (especially 24 bit) a level of -6db for peaks is perfectly acceptable. If you run the analog at +20dB you’re going to induce a lot of distortion. This whole thing is further convoluted by the fact that Mackie chooses to use 0dB as 0 on their meters instead of 0 reflecting a +4 level as is used by almost every other manufacturer. They do this so you can "marry" -10 and +4 gear all in one sysytem, sort of everything meeting in the middle. To further complicate matters, if I were in your situation, if possible, I would be going into the computer at -10 and coming out at +4 to accomodate the low headroom of the Mackies. Mackies seem to sound best when they are run at levels around -10 dB on their meters.. Kurt
     
  5. realdynamix

    realdynamix Well-Known Member

    :) Hey Kurt! I have been getting normal levels when using any analog +4db gear, but when going to a digital input I make up the gain for extra headroom using the digital input level controls to levels you said.

    Have I been doing this wrong? I don't want to over drive my analog gear just to take advantage of the extra headroom.

    --Rick
     
  6. Kurt Foster

    Kurt Foster Distinguished Member

    Rick,
    On your DATs and CDrs you will notice a little mark on the meter somewhere between -18dB and -12dB.. This is where the manufacture is referencing 0dB analog.. On a DAW, there is generally not any kind of input adjustment so you have to do any level setting at the pre amp or console.. Kurt
     
  7. downflow

    downflow Guest

    I've been tracking on my DAW with the peaks at about -2 or -1, is that too hot? I have heard that tracking at lower dB with digital gives a lower sound quality, so I was trying to track as hot as possible without clipping.
     
  8. Kurt Foster

    Kurt Foster Distinguished Member

    At 24 bit hitting -6 on individual tracks is plenty good. This leaves headroom for eq and compression at mix. When I mix, I shoot for -2dB on the 2-bus.. Kurt
     
  9. realdynamix

    realdynamix Well-Known Member

    :) Thanks Kurt, yea, I know where it lines up. But, my DAW allows gain at the AD converter, I have been using it. I have been watching the noise level on the digital meters and trying to keep it low as possible.

    This is a balancing act between the pre, output bus of the console and the AD input. I have not noticed any ill effect, you might though.

    Perhaps I should not be using any gain at the AD input, and slight compression, and gain make-up, 3db or so, to get up to a little higher average range on the digital input meter, depending on the source of course.

    Like you at 24bit, I keep the levels at the digital 2-bus at around -6. Question? What is your digital 2-bus control set at to give you that -6 at the meter, they don't always correspond because of the summing? What range do you see for the control on average?
    --Rick
     
  10. Kurt Foster

    Kurt Foster Distinguished Member

    Rick,
    I am coming out of the work station on a spdif connection to the CDr.. So whatever shows on the 2-bus meter is the same on the CDr.. Nice, huh? Kurt
     
  11. downflow

    downflow Guest

    What about on a 16 bit? Track at -6 dB and wish I had a 24 bit?
     
  12. realdynamix

    realdynamix Well-Known Member

    :) Hi Kurt! I was not clear :d:

    I am talking about mixing while in the DAW. I send out SPDIF to the burner also.

    I meant the 2-bus in your DAW. My typical (input stereo track signal) just one of many, flows like this. Analog Console/pres>(inserts if any) console 2-bus > AD (any pair of the DAW to tracks @ -6) recording/processing/mixing/editing @ 24 bit > digital 2-bus > SPDIF to burner.

    The area of my concern is what my digital 2-bus meter shows compared to what the digital 2-bus control setting shows. Are you saying...
    Regardless of the digital 2-bus control setting, the digital output meter should kick around -6, or is your control set to "0" and you are mixing to achieve the -6 reading?

    My DAW allows an attenuator before the 2-bus output control. If the control is set for "0" is the attenuator what I should be using to get the -6 on the meter?

    Sorry to babble so much, but this digital 2-bus area is a strange place in the chain.

    Thanks for your time,

    --Rick
     
  13. realdynamix

    realdynamix Well-Known Member

    :) Downflow, even though I am working with the 24bit, it provides more headroom, drops the noise floor. When I go to burn, those extra bits are ignored, this may give an appearance of less headroom when it is finally a 16 bit CD.

    But through the process of getting there, it keeps things pretty quiet preventing noise build up. If your tracks are at 16bit, then you go a little hotter. I'll leave it to Kurt to set that level, because I'm not sure where that limit would be -3, -2, ???

    --Rick
     
  14. Kurt Foster

    Kurt Foster Distinguished Member

    As I said, when I am burning a CDr @ 16 bit I try for -2db peaks. This leaves something for a ME to get a bite on. The only 16 bit multi track format I have ever used was ADAT. I would try to light up the first yellow segment on peaks (whatever that is). But on a DAW you still need to leave some room for processing no matter what bit rate you are running. Sometimes this stuff is just trial and error or as we like to call it here, between the desert and the left coast, "poke and hope" . :D Kurt
     
  15. EIK

    EIK Guest

    I meant right below +20dB on the Mackie, since that's where the yellow LED is. Somewhere right at, or around, +10dB according to the numbers, which is actually +14dB I guess?

    If "0 VU" analog = -16dB, does 10 VU = -6dB in digital, or is there a different ratio?

    If I have my drums peak at -6dB digital, many of my hits will be at -13dB or even less. This has sounded like crap in my opinion. I usually try to go as close to the 0dB in the Logic meters, as possible. Then I compress and adjust output as needed in either Waves Ren or C1.

    And how do you know which "dB" someone is talking about if they don't mention "VU"? I've seen dB mentioned many times in reference to analog. At least I think that's what they were referring to.

    I've started up using a little Audio Buddy preamp to record single channels, since it's more convenient this way. I set up a mic so the red peak light barely came on now and then. When I had the Echo Control Panel set up at -10dB it overloads, when it was set up for 4dB it peaks at around -6dB. It seems to me like this is reversed. I was thinking the Peak light on the Audio Buddy is set up for balanced connections? I used to always check the levels in Logic.

    I tried going out at "4dB" (set on Echo Control Panel). The Output Bus meter in Logic was set up with a limiter with a -3dB ceiling. Mackie showed +7dB as peaks With the Echo COntrol Panel set to "-10dB"the Mackie seemed to be peaking around -7dB (around the levels you recommended).

    Thanks,

    EIK
     
  16. Kurt Foster

    Kurt Foster Distinguished Member

    No a dB is a dB. Yes a signal at 10 dB VU on a mixer, would put you at –6 dB on the digital scale if you have calibrated the inputs. But Mackie mixers do not run on the standard +4 reference. They reference 0dB as 0dB.

    Once again, a dB is a dB. Often it will be referred to as (example) –3dB VU or – 3dB digital.


    No this is correct. At –10 the input is more sensitive.. set up to accept a lower level signal to reach 0 on the meter. Yes the audio Buddy is a +4 output. It doesn’t matter if it is balanced or not. We are discussing signal levels (voltages) not circuit topology.

    This is going to dependent on where you have attenuated the output of the Echo on the Mackie. You can run the Mackie at any level you find acceptable. It is just in the DAW on the individual tracks, that I am recommending levels of –6dB.

    This whole subject falls under the heading of “Proper Gain Structure”. The goal of gain structure is to achieve “unity gain” throughout the signal chain. This preserves proper headroom and signal to noise in all the elements in your signal chain by insuring that all the individual pieces are running at their recommended operating levels.

    To establish a proper gain structure, run a 1kHz tone into your mixer. Route the tone to the outputs of the mixer to show 0dB and then to your recorder. Calibrate the recorder to show this 0dB signal to line up to that little mark I spoke of. On a DAW there is no adjustment but this signal will probably show somewhere around –16dB. Returning to the mixer from a DAW, the output of the DAW should be adjusted to show at 0 dB on the input channel of the mixer. All your outboard should also be set to pass this signal without a significant gain or loss. This is “unity gain”. ….. Kurt
     
  17. EIK

    EIK Guest

    "Yes the audio Buddy is a +4 output. It doesn?t matter if it is balanced or not. We are discussing signal levels (voltages) not circuit topology. "



    Ok, I guess I was confused thinking that using an unbalanced -10dB connection actually sent a weaker signal than a balanced connection, hence the "dB". But I guess it has nothing to do with levels. Thanks for your everything..


    EIK
     
  18. Kurt Foster

    Kurt Foster Distinguished Member

    EIK,
    Yes a -10 signal is weaker than a +4 signal. 14dB weaker. The difference between balanced and unbalanced is that an unbalanced signal is 2 conductor [hot (+) and shield] and a balanced is 3 conductor [hot (+), cold (-) and shield]. Generally the signal is generated as an unbalanced signal and converted into balanced by spliting the hot signal and fliping it out of phase, + and - . This can then be sent down long cable runs where the two out of phase signals are combined at the reciveing end, cancelling out any noise that may have been picked up in the cable. Kurt
     
  19. ssltech

    ssltech Guest

    There are many potholes in direct comparison... F'rexample:

    Remember that 0VU is an RMS reference, on an RMS meter. 0dBFS is a peak reference, on a peak meter.

    Even constant tones will read differently between the two: the RMS value of a sine is peak value x 0.707 whereas the rms value of a square wave is 1.000 v peak value. some triangular waves will be 0.500 x peak value. These three constant tones reading the same on a VU meter will read different values (over a 6dB range) on a peak meter such as on a digital converter... similarly, the same three waveforms all reading the same on a peak meter will give a 6dB range of readings on a VU meter...

    Since in practical terms the occurence of absolute square waves and pure triangles is not all that common, the actual range of 'comparison error' to give the phenomenon a name for now, can be expected to be less than 6dB, but start recording DI's synthesizers and Fuzz guitar, and you'll certainly see these waveforms!

    The -16dB when setting up using a sine wave is a decent guideline, but to be fully informed, it's best to understand that there will be a bit of leeway.

    Comparing audio waveforms to mountain ranges, (well... why not!!!) 0dBFS is a "No mountain top shall be higher than this" ruling, and 0VU is a "the average height of the mountains is this" measurement... For mountin ranges you might be able to calculate a reasonably accurate correlation between the average height af most moountain ranges and the highest peak, but there will be variation between ranges, and sometimes the highest peak won't be all that high... bear in mind thatI'm not comparing to dynamic variation in the signal, but the shape of the waveform...

    Nika Aldrich's forum (over on pro sound web dot com) is a good place to get some more input, but do read the archives before asking the same question ahtat everyone else does!

    Cheers!
    Keith
     

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