Calibrating PPM Meters

Discussion in 'Monitoring' started by Fenben, Nov 13, 2017.

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  1. Fenben

    Fenben Active Member

    Joined:
    Nov 13, 2017
    Location:
    UK
    Hello

    I am a newbie to this forum so please bear with me. I am a freelance TV and Radio producer and have worked in BBC radio studios and edit suites for over 20 years, so I have an penchant for the good old fashiond PPM meters. I also do corporate/charity work at home using Premier Pro on an Mac Pro. Premierhas it's own audio meters built in, but when an opportunity came along to pick up a set of PPM's I took it and so have a set of Sifam 74A PPM Meters (see pic below).

    IMG_8426.jpg

    My plan was to take a feed from my line out to the meters and a digital feed to my amp for monitoring purposes. The output of the line out can simply be controlled by the macs volume control.

    This all works fine, but when I send tone at 0db with volume set to max, it registers as 3 instead of 4. I have looked into ways of eeking that extra 6db out of my mac (Boom 2. sound booser etc) but they seem to cause more complications than they solve.

    Another option is that I physically adjust the meter so that they match the mac. I have 2 questions:

    1) is there a reliable software way that I can get that extra 6db?
    2) if I was to manually adjust the needle, where would I fid the relevant screw to turn (there are no adjustment screws on the front of the meters).

    Thanks in advance

    Andrew
     
  2. Boswell

    Boswell Moderator Distinguished Member

    Joined:
    Apr 19, 2006
    Location:
    UK
    Home Page:
    Hi, and welcome!

    Where did you get the figure of an "extra 6dB" from? The scale readings on a PPM and a VU meter fed with the same steady-state tone do not correspond. So, for example, a sinewave measured separately at -10dBu changing to 0dBu should show these levels on a +4VU meter, but will go from 2.5 to 5 on a PPM set to BBC scales (like yours). One unit difference on a BBC PPM is 4dB.

    Here is a graphic taken from an SOS article showing how three different PPM calibrations compare with +4VU, 0VU and other steady-state level measurements:

    upload_2017-11-13_18-47-51.png
     
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  3. Fenben

    Fenben Active Member

    Joined:
    Nov 13, 2017
    Location:
    UK
    Sorry, my mistake. I thought I had read it was 6db, but I can see from your graphic that is actually 4db. Thanks. Nice infographic.
     
    audiokid likes this.
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    The New AT5047 Premier Studio Microphone Purity Transformed

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