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Post by mrholmes on Jan 26, 2020 20:40:40 GMT -6
Just because its so much fun setting VU meters.
In the analog domain zero VU is set to 1.224 Volts. I get this I can measure this at the output of my interface with an 1 khz sine wave and set my analog VU meters.
Now comes the confusion if you run a hybrid system, as the most studios do today.
PlugIn companies say zero VU equals -18 dbfs in the DAW. Try the same with a 1 khz sine wave and voila zero VU is equal to - 18 dbfs.
But hej ho outside the DAW my converter output is set to read 1.224 Volt at about - 9 dbfs.
It's a difference of -9 dbfs.
I deal with this now with my I/O plug in input output gain setting.
But every time I set a new VU meter to zero I ask myself why is the whole confusion? Can't we set a standard to this problem, or at least a metering that reads equal inside and outside the DAW.
I often forget it or wonder what happened to the levels etc. Then I need to remind myself that its not reading the same in and outside the DAW.
Running hybrid levels should be easier to handle.
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Post by Blackdawg on Jan 26, 2020 21:56:43 GMT -6
Most convters you can change the calibration with a click to reference -24, -20(sometimes), -18 are the big choices. But some do all the way to -9 as well.
Would check the manual on your converters.
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Post by mrholmes on Jan 26, 2020 22:31:54 GMT -6
Most convters you can change the calibration with a click to reference -24, -20(sometimes), -18 are the big choices. But some do all the way to -9 as well. Would check the manual on your converters. That would be cool.... |
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Post by mrholmes on Jan 27, 2020 8:24:38 GMT -6
Most convters you can change the calibration with a click to reference -24, -20(sometimes), -18 are the big choices. But some do all the way to -9 as well. Would check the manual on your converters.
Good advice but non of the output settings reach 1.224 Volts when internal zero VU is - 18 dbfs
RME just offers 3 Settings.
Hi GAIN + 4 dbu = 1.224 Volts ?
- 10 dbv
It stays the old way.
I need to remember that zero VU outside the DAW is internal + 9 dbfs on top.
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Post by matt@IAA on Jan 27, 2020 9:19:46 GMT -6
Yeah, the relationship between dBu and dBFS is totally driven by your converters. The internal 0VU is “gear dependent”. But, then again, the external 0VU is gear dependent. You could recal external meters to a different 0VU point than +4 dBu. How you set each meter depends on if you’re trying to monitor headroom on each piece or on the overall chain.
To have zero VU internal = -18 dBFS means your converter 0dBFS is +22 dBu. I believe that’s static based on the hardware.
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Post by christopher on Jan 27, 2020 10:12:20 GMT -6
My old fireface cant do +22dB, I believe it’s because most of the best ADC codec chips are designed for consumer audio? So in order to get to +22dB they would have had to add another little amp stage. RME chose not to care, but that might be why they sound so clear? High gain’ is the best setting, I think -15dBfs = 1.2v? +4 on RME isn’t the best way to go
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Post by mrholmes on Jan 27, 2020 10:19:30 GMT -6
Yeah, the relationship between dBu and dBFS is totally driven by your converters. The internal 0VU is “gear dependent”. But, then again, the external 0VU is gear dependent. You could recal external meters to a different 0VU point than +4 dBu. How you set each meter depends on if you’re trying to monitor headroom on each piece or on the overall chain. To have zero VU internal = -18 dBFS means your converter 0dBFS is +22 dBu. I believe that’s static based on the hardware. This clears up things a bit... They say the converters run at +4dbu = 1.224 Volts... and I have hardware that says this too... -18 dbfs ≠ 1.224 Volts + 4 dbu on the interface outputs.
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Post by svart on Jan 27, 2020 10:36:04 GMT -6
There are no impedance standards in audio, and thus no true analog interface standards. 1.224V into what impedance? Are you measuring RMS or peak? Is the DBFS scale in your DAW based on RMS+3dB, true peak or hybrid of the two?
As Dogears pointed out, DBFS means absolutely NOTHING to the converters. It's just a measure of the digital peak level relative to the bits as encoded. It's completely arbitrary how it relates to A/D and D/A and can scale differently from device to device.
That's why folks do the "meter calibration" stuff, is because there are no true interface standards in audio and there is no way to know what you're getting without doing it.
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Post by christopher on Jan 27, 2020 11:26:56 GMT -6
It’s a pretty interesting and very confusing topic that I constantly like to revisit. I just saw this video where Rupert Neve claims he and his engineer Jeff Watts invented the dBu.. he doesn’t claim the u to mean ‘unweighted’, but it’s a reference to units of volume on a VU meter. Wow. So really a dBu should be in reference to the load of a VU meter. I guess the world didn’t get the memo lol
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Post by stormymondays on Jan 27, 2020 15:11:23 GMT -6
The RME is a bit of a pain, but I solved this a while ago. Here's the info:
-First, ignore the "+4 dBU" setting because it's NOT +4 dBU at all. People have argued about this in the RME forums but the developers are very opinionated.
-The "real" +4 dBU setting is the High Gain / Low Gain (depending on whether it's input or output). Once set to these settings, the interface is calibrated to -15 dBFS = 0VU.
When interfacing with external gear with Logic's I/O plugin I have a +3 (output) -3 (input) gain setting. This way, a -18 dBFS signal in Logic will be bumped to -15 dBFS on the way out, which RME makes it 0 VU. And the reverse for the input. A 0 VU signal will hit the converters and get a -15 dBFS input into Logic, which is then knocked down -3 dB so it becomes -18 dBFS.
I suppose I could have picked up -15 dBFS as my 0 VU and not do any offsets, but I decided to keep the -18 dBFS reference.
Some time later, I added a Focusrite Clarett Octopre. This interface is crazier, because it has different Input and Output voltages, and even the published specs are wrong. For that one to work correctly I have to set +4 Output and +3 Input in the I/O plugin.
Hope this helps!
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Post by matt@IAA on Jan 27, 2020 15:57:19 GMT -6
It’s a pretty interesting and very confusing topic that I constantly like to revisit. I just saw this video where Rupert Neve claims he and his engineer Jeff Watts invented the dBu.. he doesn’t claim the u to mean ‘unweighted’, but it’s a reference to units of volume on a VU meter. Wow. So really a dBu should be in reference to the load of a VU meter. I guess the world didn’t get the memo lol That makes my head hurt, because as far as I know 0VU is defined in terms of power ratio! In other words 0VU = +4 dBm = 1 mW. But +4 dBu = +4 dBm only when the load is 600 ohms. Again, as far as I know a "real" VU meter only works for 600 ohms. +4 dBu into 10k is -8.2 dBm!  |
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Post by mrholmes on Jan 27, 2020 18:05:45 GMT -6
The RME is a bit of a pain, but I solved this a while ago. Here's the info: -First, ignore the "+4 dBU" setting because it's NOT +4 dBU at all. People have argued about this in the RME forums but the developers are very opinionated. -The "real" +4 dBU setting is the High Gain / Low Gain (depending on whether it's input or output). Once set to these settings, the interface is calibrated to -15 dBFS = 0VU. When interfacing with external gear with Logic's I/O plugin I have a +3 (output) -3 (input) gain setting. This way, a -18 dBFS signal in Logic will be bumped to -15 dBFS on the way out, which RME makes it 0 VU. And the reverse for the input. A 0 VU signal will hit the converters and get a -15 dBFS input into Logic, which is then knocked down -3 dB so it becomes -18 dBFS. I suppose I could have picked up -15 dBFS as my 0 VU and not do any offsets, but I decided to keep the -18 dBFS reference. Some time later, I added a Focusrite Clarett Octopre. This interface is crazier, because it has different Input and Output voltages, and even the published specs are wrong. For that one to work correctly I have to set +4 Output and +3 Input in the I/O plugin. Hope this helps!
AMEN THANK YOU @stromymondays
Now I have the same gain structure throughout the whole system.
They really messed the settings up at RME + 4 dbu is not 1.224 Volts but it should be. The best of it all for the inputs it's the opposite the LOW GAIN setting is the one that makes in and output level equal.
For ADAT extensions it needed very different settings, for a reason I don't know they have 3 db lesser headroom.
THE industry should set a standard for this even if dbfs means nothing at all.
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Post by mrholmes on Jan 27, 2020 18:07:12 GMT -6
It’s a pretty interesting and very confusing topic that I constantly like to revisit. I just saw this video where Rupert Neve claims he and his engineer Jeff Watts invented the dBu.. he doesn’t claim the u to mean ‘unweighted’, but it’s a reference to units of volume on a VU meter. Wow. So really a dBu should be in reference to the load of a VU meter. I guess the world didn’t get the memo lol That makes my head hurt, because as far as I know 0VU is defined in terms of power ratio! In other words 0VU = +4 dBm = 1 mW. But +4 dBu = +4 dBm only when the load is 600 ohms. Again, as far as I know a "real" VU meter only works for 600 ohms. +4 dBu into 10k is -8.2 dBm!
That sounds to my ears what Bob Katz wrote - confusion with numbers - at least it always confuses me...
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Post by christopher on Jan 28, 2020 11:12:59 GMT -6
It’s a pretty interesting and very confusing topic that I constantly like to revisit. I just saw this video where Rupert Neve claims he and his engineer Jeff Watts invented the dBu.. he doesn’t claim the u to mean ‘unweighted’, but it’s a reference to units of volume on a VU meter. Wow. So really a dBu should be in reference to the load of a VU meter. I guess the world didn’t get the memo lol That makes my head hurt, because as far as I know 0VU is defined in terms of power ratio! In other words 0VU = +4 dBm = 1 mW. But +4 dBu = +4 dBm only when the load is 600 ohms. Again, as far as I know a "real" VU meter only works for 600 ohms. +4 dBu into 10k is -8.2 dBm! I think that’s maybe why bridging became the standard? If you only need -8.2dBm to send the ‘same’ signal to a channel that a +4dBm needed.. now you need less power, cheaper to build, low power IC chips work easier etc. I’m just guessing that’s how it works. I know that the power companies manipulate ohms law to send power long distances, that’s why there’s 30,000 volt lines. I figure audio bridging is kind of similar? To me 600:600 gear is always my favorite though. My subjective opinion is that pushing power instead of bridging gives a fatter sound...(shrug) |
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Post by matt@IAA on Jan 28, 2020 12:06:01 GMT -6
Oh, absolutely. For maximum power transfer you want matched impedance. For maximum efficiency you want infinite load vs source. For us, power doesn’t mean anything, so there’s no good reason to worry about matching. But some gear is optimized for specific impedances.
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