Input Trim – 0dB is not always 0dB

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This topic contains 4 replies, has 2 voices, and was last updated by Profile photo of Jay Jay 4 years ago.

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  • #62334
    Profile photo of Jay
    Jay
    Participant

    FW 1.40, 1.41. Didn’t check earlier versions.

    I noticed some minor level variations in working with a single track across different channels and think I’ve narrowed it down to an offset issue with input trim.

    Observed on input trim:
    – For a given input signal (sine wave), if trim is set at 0dB and has never been taken past -24/+24 limits then you get a “0dB” out of trim. Base reference.
    – If you take trim past -24 (it stops at -24) and back to 0dB, the output signal is about 1/2dB higher than 0dB ref.
    – If you take trim past +24 (it stops at +24) and back to 0dB, the output signal is about 1/2dB lower than 0dB ref.

    I have yet to find a way to “reset” this channel back to the 0dB reference short of recalling the scene or show. If you save it with the trim offset then the scene/show will forever have the offset.

    As an aside, I have some PEQ gains that I can’t get to read 0dB that appear to be behaving in a similar fashion but are at least displaying the fraction gain offset (.1).

    Jay

    #62338
    Profile photo of SteffenR
    SteffenR
    Participant

    how you measure it?

    #62344
    Profile photo of Jay
    Jay
    Participant

    SMAART v7 – It showed up as I was measuring consistency across different analog inputs, which initially looked like the A/D side but it stuck with an input channel.

    Dante In / Dante Out also showed it in SMAART.

    Unfortunately, I just went to take screen shots for you and can’t duplicate it now that I restarted the system and loaded a clean show.

    What does show up (easily viewed – no audio):

    If you take a channel that hasn’t been slammed on trim, you have -1.1, -0.5, 0.0, +0.5, +1.1.

    Set Trim to 0, turn to +24, and back to zero. You can set -1.3, -0.7, 0.0, +0.3, +0.9.
    Set Trim to 0, turn to -24, and back to zero. You now can set -0.9, -0.3, 0.0, +0.7, +1.3

    I can’t duplicate it in audio right now, but looking at the displayed values it looks like “0” has shifted. Similar to the PEQ comment I made above. Based on the shift above, it looks more like a .2dB shift.

    Can anyone else duplicate the apparent shift in offset for trim?

    Jay

    #62370
    Profile photo of SteffenR
    SteffenR
    Participant

    What is your system?

    #62372
    Profile photo of Jay
    Jay
    Participant

    DM64, S5000, Dante in Slot 4

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