O
ofajen
Daddy-O Daddy-O Baby
I noticed a few weird things last week and spent several hours over several days sorting them out, pestering Bob Katz several times in doing so.
The puzzles:
1) Why did Bob's -20 dB pink noise file not register at 0 VU, when I thought I had -20 dB FS calibrated as 0 VU on the meters on my main outputs using Live 6's test tone calibration?
2) Why did Roger Nichols' free Inspector plug in actually show an RMS value of - 23 dBFS when playing Bob's -20 dB pink noise file?
3) Why did it look, at first glance, as though Inspector was showing a value of -20 dBFS on the pink noise file, but actually wasn't?
Rather than bore you with the pain and confusion of figuring it out, I'll just give you all the answers:
1) The test signals didn't show up as 0 VU because Live 6's test tone function is off by about 6 dB, i.e. the tone is actually 6 dB too hot. Don't use it, use a properly calibrated test file instead, or at least be aware that the signal is 6 dB hotter than indicated. I'm sure there are many such test files available, but if you need them, Bob keeps a -20 dBFS pink noise file on his site (digido.com) and Presonus has a -18 dBFS 1 KHz sine tone test file on their site.
2) While Inspector XL gives you the "peak/RMS parity" option, the free Inspector plug in does not, so the RMS values are referenced to the RMS value for a full scale square wave, not a full scale sine tone. That means that RMS values will always be "mathematically correct" but will also always be 3 dB below what international standard practices call for. In particular, a sine tone will show an RMS value 3 dB below its peak value. Most high end digital meters use the IEC standard where the RMS value is referenced to a full scale sine tone, meaning that sine waves will have the same reading on peak and RMS. Thus, using the free Inspector plug in, Bob's -20 dBFS noise file shows up as -23 dB, since the RMS reference used is 3 dB higher than standard practice.
3) The Inspector plug in seemed to show a value of -20 dB on the pink noise file at first glance because there is an error in the scale markings on the plug-in's meter. The only marking between -18 dB and -30 dB is labeled as -21 dB, but in fact it is actually -24 dBFS! So the reading was 1 dB above that marking, but actually turned out to be -23 dB, not -20 dB!
I thought I would share these little insights in case anyone else is using these programs and wanting to actually have everything knocked totally flat in terms of level practices.
Cheers,
Otto
The puzzles:
1) Why did Bob's -20 dB pink noise file not register at 0 VU, when I thought I had -20 dB FS calibrated as 0 VU on the meters on my main outputs using Live 6's test tone calibration?
2) Why did Roger Nichols' free Inspector plug in actually show an RMS value of - 23 dBFS when playing Bob's -20 dB pink noise file?
3) Why did it look, at first glance, as though Inspector was showing a value of -20 dBFS on the pink noise file, but actually wasn't?
Rather than bore you with the pain and confusion of figuring it out, I'll just give you all the answers:
1) The test signals didn't show up as 0 VU because Live 6's test tone function is off by about 6 dB, i.e. the tone is actually 6 dB too hot. Don't use it, use a properly calibrated test file instead, or at least be aware that the signal is 6 dB hotter than indicated. I'm sure there are many such test files available, but if you need them, Bob keeps a -20 dBFS pink noise file on his site (digido.com) and Presonus has a -18 dBFS 1 KHz sine tone test file on their site.
2) While Inspector XL gives you the "peak/RMS parity" option, the free Inspector plug in does not, so the RMS values are referenced to the RMS value for a full scale square wave, not a full scale sine tone. That means that RMS values will always be "mathematically correct" but will also always be 3 dB below what international standard practices call for. In particular, a sine tone will show an RMS value 3 dB below its peak value. Most high end digital meters use the IEC standard where the RMS value is referenced to a full scale sine tone, meaning that sine waves will have the same reading on peak and RMS. Thus, using the free Inspector plug in, Bob's -20 dBFS noise file shows up as -23 dB, since the RMS reference used is 3 dB higher than standard practice.
3) The Inspector plug in seemed to show a value of -20 dB on the pink noise file at first glance because there is an error in the scale markings on the plug-in's meter. The only marking between -18 dB and -30 dB is labeled as -21 dB, but in fact it is actually -24 dBFS! So the reading was 1 dB above that marking, but actually turned out to be -23 dB, not -20 dB!
I thought I would share these little insights in case anyone else is using these programs and wanting to actually have everything knocked totally flat in terms of level practices.
Cheers,
Otto
