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-10 or +4, Whats it to Me?
Old 17th May 2006
  #1
Gear Maniac
 

-10 or +4, Whats it to Me?

The manual for my 24 ch Soundcraft Spirit Auto says "All input Tape Sends are factory set to suit -10dBV equipment. If a level of +4dBu is required the output level may be changed by removing resistors R130/R131 from the Input PCB."
I am using the Tape Send on each chanel directly into my Alesis HD24. Is this change something I need to consider doing? Its working as it is right now & everything sounds ok, but I seem to be running the individual chanel gains pretty high. I did use the search function, but could find no clear answer. In fairness, none of this is very clear to me! A clarification is definately in order.
I posted this question over at Tapeop also.
Old 17th May 2006
  #2
Gear Maniac
 

I might add that my aux's have to be run at extremely high level, almost dimed, in order to get adequate signal to the headphone amp.
Old 17th May 2006
  #3
Lives for gear
 

Most consumer and semi-pro tape decks would use the lower -10 level, which is probably why they default to this. I guess they are unbalanced outputs too?

It's a bit of a shame, because the HD24 has balanced +4 inputs. So not only is the level too low, you aren't making use of balanced cables for reduced noise.

I guess raising it's output by doing that mod would help a little. But maybe you should look at a better solution.

How many channels do you actually track at once? For the critical stuff, maybe you should go direct from a standalone mic preamp into the HD24, staying with balanced +4 all the way.
Old 17th May 2006
  #4
Gear Head
 

Why the hell are you using the TAPE sends ??? use the mains out or the individual ch outs theyre at +4 Humm

Later
Buzz
PS: it's 14db
Old 18th May 2006
  #5
Gear Maniac
 

Im using the tape sends & returns because I record bands live in my studio. Usually 12 to 16 tracks at once. I record directly to the HD24 and mix ITB. All of my cables are new balanced Gotham cables. All sends & recieves on the board are balanced. One of the guys at Tapeop helped me answer my question. I will me making the simple mod to the board this weekend to make it all +4. This board was made in the early 90's. most consumer tape decks at the time were using -10 RCA jacks for in's & out's. This board was capable of working in a consumer or a pro invironment.
There is a manual available at the Soundcraft website. The mixer is a Soundcraft Spirit Auto.
Thanks for your help!
Old 18th May 2006
  #6
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P.S.S

The differnce is not 14 dB. Remember, the dB scale is logarithmic. That would leave the difference between -10 and +4 to be 11.8dB.

heh
Old 18th May 2006
  #7
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theblotted's Avatar
 

Quote:
Originally Posted by Nerdyrocker
P.S.S

The differnce is not 14 dB. Remember, the dB scale is logarithmic. That would leave the difference between -10 and +4 to be 11.8dB.

heh

Nerdy indeedheh
Old 18th May 2006
  #8
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by Nerdyrocker
P.S.S

The differnce is not 14 dB. Remember, the dB scale is logarithmic. That would leave the difference between -10 and +4 to be 11.8dB.

heh
It would be 14db, if both signals are reference dbv.
Old 30th October 2008
  #9
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memphisindie's Avatar
 

The Spirit Recording version is balanced, servo balanced, all ins and outs including the tape sends and recieves, at -10 or +4.
It is an inline board with a separate monitor path per channel.
We did the "un-mod" and it made a huge difference, but, the power supply, chip, and cap upgrade is even more dramatic.
I did it to mine Bluesman, and it rocks!!
Old 30th October 2008
  #10
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Rick Sutton's Avatar
 

Quote:
Originally Posted by Nerdyrocker View Post
The differnce is not 14 dB. Remember, the dB scale is logarithmic. That would leave the difference between -10 and +4 to be 11.8dB.
Must be the "new math".
Which is now the "old math".
Which is the "wrong math".heh
Old 30th October 2008
  #11
Lives for gear
 

It's still a 14 db difference, but think of it this way:

+4db is 1.23V
-10db is 0.316V
Old 30th October 2008
  #12
Gear Addict
 
The Reel Thing's Avatar
 

what they call - 10 dB are usually -10 dBa
what they call + 4 dB are usually +4 dBu
dBa and dBu have different references, so the difference is NOT 14 dB.

the difference in level on the meter is 6 dB. this is also the difference between an unbalanced and a balanced signal through a transformer.

yes, i would definitely modify the console to +4 dBu, if you really want to stick with a Spirit. besides having a balanced signal flow you would lower the noise floor by 6 dB on every output.

tom

analoghaus :: studio label verlag - home
Old 30th October 2008
  #13
Quote:
Originally Posted by nosebleedaudio View Post
It would be 14db, if both signals are reference dbv.
But they're not - it's +4dBu, but -10dBv. As I'm sure you're aware, dB in itself is just a ratio - with no qualifying reference, it's meaningless as an absolute value.

dBA is a weighted curve, forget what the reference is (it's a sound pressure level rather than an electrical level) but is scaled to better reflect the sensitivities of human hearing.
Old 30th October 2008
  #14
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memphisindie's Avatar
 

Quote:
Originally Posted by psycho_monkey View Post
But they're not - it's +4dBu, but -10dBv. As I'm sure you're aware, dB in itself is just a ratio - with no qualifying reference, it's meaningless as an absolute value.

dBA is a weighted curve, forget what the reference is (it's a sound pressure level rather than an electrical level) but is scaled to better reflect the sensitivities of human hearing.
Either way, it's not something you think about when you calibrate the 2", you just look at the meters and go up 14db, dontcha? Yeah ya do.
Old 30th October 2008
  #15
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by memphisindie View Post
Either way, it's not something you think about when you calibrate the 2", you just look at the meters and go up 14db, dontcha? Yeah ya do.
Just about everybody is correct.
0dbV= 1volt RMS
0dbm or dbu = .775V RMS
And you can make a meter read what ever you want, not a good idea in some applications..
Old 30th October 2008
  #16
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Ben B's Avatar
 

Quote:
Originally Posted by Nerdyrocker View Post
P.S.S

The differnce is not 14 dB. Remember, the dB scale is logarithmic. That would leave the difference between -10 and +4 to be 11.8dB.

heh
This is correct. 20 log 1.23V/0.316V = 11.8dB.

-Ben B
Old 30th October 2008
  #17
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Ben B's Avatar
 

Quote:
Originally Posted by memphisindie View Post
Either way, it's not something you think about when you calibrate the 2", you just look at the meters and go up 14db, dontcha? Yeah ya do.
How high do the VU meters go on your 2" deck?

Besides, no.

-Ben B
Old 30th October 2008
  #18
Quote:
Originally Posted by memphisindie View Post
Either way, it's not something you think about when you calibrate the 2", you just look at the meters and go up 14db, dontcha? Yeah ya do.
I can't ever recall using a 2" that had -10dBV i/o!
Old 30th October 2008
  #19
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It's dB not db and the difference in voltage between +4dBu and -10dBV is 11dB (give or take a tenth of a dB or so).


/Peter
Old 30th October 2008
  #20
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nosebleedaudio's Avatar
 

Pro has always been +4dbm.
Most gear that uses the -10dbV is cassette decks, CD players ect, but even most of those are capable of a +20dbm and greater output level.
Old 30th October 2008
  #21
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Mike, dB dB dB!


/Peter
Old 30th October 2008
  #22
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by Audiop View Post
Mike, dB dB dB!


/Peter
OK OK OK but it MEANS the same thing...
Old 30th October 2008
  #23
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Sorry for being so stiff but IMO it's important to use the right symbols and names for stuff when it comes to technical stuff and science. You know what you mean and I know what you mean, but a novice trying to learn about dB, dBu, dBV, mV, Pa, Hz, kHz, amperes, power, spectrum, Kelvin and yada yada it can be very confusing to see the same stuff go under different names or symbols.

Keeping to the SI-system is a wise thing IMO when it comes to engineering and science-oriented stuff.




/Peter
Old 30th October 2008
  #24
Quote:
Originally Posted by Audiop View Post
Sorry for being so stiff but IMO it's important to use the right symbols and names for stuff when it comes to technical stuff and science. You know what you mean and I know what you mean, but a novice trying to learn about dB, dBu, dBV, mV, Pa, Hz, kHz, amperes, power, spectrum, Kelvin and yada yada it can be very confusing to see the same stuff go under different names or symbols.

Keeping to the SI-system is a wise thing IMO when it comes to engineering and science-oriented stuff.




/Peter
+1 - it's anal but useful!

deciBel - the Bel is the unit.

After all - Gb is a Giga-bit, not a Giga-byte (GB) - you'd be quite disappointed to find your computer only had 4 giga-bits of ram!
Old 30th October 2008
  #25
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Yes these things are complicated enough as it is.. and it shows in this very thread.


/Peter
Old 30th October 2008
  #26
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by Audiop View Post
Yes these things are complicated enough as it is.. and it shows in this very thread.


/Peter
I was not offended, but to me there is far more incorrect info on forums than an upper/lower case thing.
But you are right, getting in the habit is another story.
My biggest problem is IM NOT a good typist, the old two finger method...
Old 30th October 2008
  #27
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Agree and in no way I meant anything ill. :-)


/Peter
Old 30th October 2008
  #28
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memphisindie's Avatar
 

What happens when you're calibrating before a session and in one channel you adjust and go over, it resets back to a lower level,,, to minus ten, no, maybe, doesn't matter where because you're not calibrating to that, but, no one ever said that a 2" was set at -10 as a standard. Wasn't even worth mentioning, but, I did.
I'm naughty.
Old 30th October 2008
  #29
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FeatheredSerpent's Avatar
 

'dBvu' gets written all over the place on this forum, being ignorant, I did some reading and so is it right to say that 0dBvu is the same as saying dBv OR dBu, 'dBv' being the older way to espress it and dBu the newer?
So this common 'dBvu' is just a habit of tying the two together, because there can still be confusion with dBV, or what?
Old 30th October 2008
  #30
Quote:
Originally Posted by FeatheredSerpent View Post
'dBvu' gets written all over the place on this forum, being ignorant, I did some reading and so is it right to say that 0dBvu is the same as saying dBv OR dBu, 'dBv' being the older way to espress it and dBu the newer?
So this common 'dBvu' is just a habit of tying the two together, because there can still be confusion with dBV, or what?
dBVU is another reference - I can't remember offhand what to. VU orvolume unit are what your mixing desk shows. Not your Daw though - that uses dBFs - which is the level related to all bits on, ie full scale, and so dBFs signals are always negative (you can't have louder than full scale, and the log of a value less than 1 is negative.
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