antispatula said:
Fist off, I'd like to thank everyone whos helped me start to get the calibration process, it's all slooooowly coming into focus.
So let me get this strait. The VU meter= Signal of MRL tape-Signal of tape going to be used.
So if I get an MRL tape recorded at 0 DB and use 456, that's 0-6, so I want to have all VU meters at -6 keeping in mind I want to follow the Max Op level rule and get as close as I can to best sound without reaching distortion. Is this right?
And it has been discussed that it's better to have a few DB headroom, 3 DB, so does that mean it would be wise for me to set the channels to -3 DB?
Oh and one more thing for now.......When I connect a volt meter to the outs, how? I have no idea......Do I actually stick the leads in the XLR out's or something?! I hae no idea. Thanks!
If you can answer ANY of these, please do!
OK, here are some thoughts and a Key point of information. First the Key point:
dB is the measure of the ratio of 2 values.
When we say -3 dB (3 dB down) we are saying that the measured level is 3 dB smaller than the reference.
You will see dBm and dBv. The m and v just tell you what reference us being used.
0 VU is defined as the level that you get from tape that has been recorded at 185 nW/m. This is historic due to the capabilities of the tape some 40 years ago. Go over that level and you headed into distortion etc.
So a +6 dB tape has better properties and can record a much stronger signal without distortion.
Rather than calibrate your VU meters to read 0 VU at 185 nW/m and record with the VU meters reading + 6 VU we set the meters to read 0 VU when in fact they are measuring a signal that is + 6 dB over the 185 nW/m level. Think of +6 as an offset.
MRL tapes have been recorded at many different levels. You can claibrate using any of them if you use the proper offseet. Quantegy has a calculator at:
http://www.quantegy.com/html/recordersetup.html
Let's say that you have a +6 MRL tape. The level on the tape has been recorded at + 6 dB above the 185 nW/m reference. This means that the tape level is 370 nW/m ( a nano weber per meter is a measurement of magnetic flux).
The goal of calibration is to cause the the deck to read 0 VU when playing the 370 nW/m reference and to output the decks 0 VU voltage level. Many consumer decks use -10 dBv as their 0 VU "line" level. 0 dBv is 1 volt and -10 dBv is 0.316 volts (( 20 log(1/0.316) = 10 dB ))
Each deck has its own signal paths so you will need to follow the instructions for that deck to get the calibration chain correct. Oh and I should add that many Tascam/teac decks will not be able to calibrate to 370 nW/m. Tey just cannot put out enough signal to the heads or adjust down enough. Thats OK you can calibrate to +3 (250 nW/m reads 0 VU) and have more headroom.
That is playback calibration. record calibration is just the reverse. (on a 370 nW/m deck) you want a 0 vu input signal (0.316 volts input to the jacks) to read 0 dB and put 370 nW/m on the tape. (It then would playback with a 0 VU reading).
Sorry about the long winded rambelings.
As for your meter. Just build an adaptor plug. I take an old plug and tape the wires to the meter probes.
Regards
PS Just reread your post and realized that you know all this. Egg on my face. I'll leave the post as is so that other who do not know will see it.
