Levels question: +4dBu mixer output to Qu input is 6 db lower

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This topic contains 11 replies, has 7 voices, and was last updated by Profile photo of Alex A&H Alex A&H 1 year, 11 months ago.

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  • #57061
    Profile photo of mangobob
    mangobob
    Participant

    I want to use the Qu-Pac as a standalone recorder. On an analog mixer, I have a 1kHz test tone reading 0db on the meters. Going out the +4dBU balanced master out via balanced cable into Qu-Pac line input 1, the Qu channel meter reads -6db.. in other words I need to add 6db of gain on the Qu preamp to match the levels coming from the mixer.

    Shouldn’t 0db on the mixer equal 0db on the Qu’s meters? When I run into stereo line input ST1 with preamp set flat it correctly reads 0 with the Qu preamp gain set flat.

    Is there a hardware difference between the regular and stereo line ins? Which one would be better suited for recording main mix coming from the analog mixer?

    #57066
    Profile photo of Nicola A&H
    Nicola A&H
    Keymaster

    Hi mangobob,

    The Mono Line Inputs on Qu mixers have a built-in 10dB pad (attenuation). So your +4dBu output -10dB pad +6dB gain = 0dB on the meters.

    Hope this helps.

    #57095
    Profile photo of mangobob
    mangobob
    Participant

    Ahh.. this -10dB line input pad isn’t documented in the manual.

    Further testing confirms +10dB of channel gain is required for analog mixer 0 VU = Qu 0 VU (got a more accurate figure ensuring analog mixer was set to unity gain and then reading recorded values instead of eyeballing the Qu meters).

    For recording analog mixer’s balanced +4dBU direct outs into the Qu, which is the better option:

    1) Signal into Qu TRS Line inputs with +10db Qu preamp gain applied to negate the pad and line everything up
    2) Signal into Qu XLR Mic inputs to avoid the 10db pad

    Is the pad and extra makeup gain really that big of a deal in a studio recording context? Can the Qu Mic inputs handle a balanced line signal.. or could there be some sort of impedance problem? The analog mixer says the channel direct outs are “100 ohm Impedance-Balanced”.

    I’m thinking option 1 is the way to go.

    #57099
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    Option 1 – the mic inputs are not the place for a line level signal.

    The pad and subsequent gain won’t hurt significantly (of course you could boost the signal from the analogue desk – but I imagine that would change the dynamic more than the pad would). Just consider it a different number for zero 😉

    #57138
    Profile photo of Dr. J
    Dr. J
    Participant

    Nicola – can you tell us some of the finer details of the QU mixers that is not in the manual. For example – how much mix bus summing room do we have?

    If I use pink noise into a channel (PFL’d) with the fader at Unity & apply gain until it reads meter 0dBu – once I un-PFL the channel and look at my main meter it is -3dBu down. Of course my master fader is at unity but the meter reads -3dBu down. So there is some sort of built in pad/protection there?

    I would like to know some of the finer details if you know and don’t mind sharing with us.

    Thanks!

    #57142
    Profile photo of [XAP]Bob
    [XAP]Bob
    Participant

    I’d be interested as well – I kind of assumed that internals would be floating point, giving virtually unlimited dynamic range, but that’s not necessarily the case of course.

    #57159
    Profile photo of Nicola A&H
    Nicola A&H
    Keymaster

    The internal processing is fixed point. There is 18dB of headroom.

    Dr.J – I think what you are seeing is a result of the PAN law. If you pan fully left you should get the same meter reading on the master left as you have on the input. Also I’d recommend using a sine wave (not pink noise) for level alignment in a mixing console.

    #57314
    Profile photo of mangobob
    mangobob
    Participant

    I noticed the ST1 & ST2 inputs do not have this -10dB pad (if you look at the System Block Diagram you can see the resistors missing compared to the Line 1-16 inputs).

    Is the ADC chip on ST1 & ST2 the same as Line 1-16? Or is there a difference in converters for the stereo signals?

    #57320
    Profile photo of Andreas
    Andreas
    Moderator

    According to both the block diagram and the specs ST inputs differ significantly from channel inputs.
    The do not have an analog gain, just a digital trim. ST1/2 are normalized to +4dBu, ST3 has a nominal input level of 0dBu (and max levels of +22dBu/+18dBu respectively).
    I guess converters are same, but analog circuit obviously is different.

    #57322
    Profile photo of mangobob
    mangobob
    Participant

    Which is better quality for recording main stereo mix bus from outboard mixer (via 100 ohm symmetrically balanced output)? Obviously not ST3 since it’s unbalanced. Hopefully someone from A&H can chime in on ST1/2 vs Line Inputs.

    #83769
    Profile photo of moon
    moon
    Participant

    Is that also true on the SQ5 mixers ?

    #83798
    Profile photo of Alex A&H
    Alex A&H
    Keymaster

    Hi Moon,

    The line inputs (ST1, 2 & 3) work in the same way as the Qu series, as does the Pan law.

    As the SQ preamps have a pad control, the line inputs are not needed.

    Thanks!

    Alex

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