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Old 21st January 2012, 11:34 AM   #1211
DF96 is offline DF96  England
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Quote:
Originally Posted by BNFY
Guys that live in the "other" world, Wireless and RF, tend to think in terms of power, not voltage. They always use 10 log ratio, not 20. But for audio voltage measurements, it should be 20 of course.
It should be 20 for any voltage measurements, because we are actually talking about power. 0.01% (voltage) distortion is -80dB whether audio, RF or anything else. Guys in that other world use 10 or 20, as appropriate, if they know what they are doing.

A few weeks ago we had a dB argument on a radio forum - I was astonished how confused some people were and how confidently they were wrong; please let's not have one here too.
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Old 21st January 2012, 12:01 PM   #1212
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Guess what opamps are used inside the Metric Halo ULN/LIO-8 "soundcards", to many the most transparent sounding pro-audio interfaces they ever got their hands on.
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Old 21st January 2012, 02:13 PM   #1213
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Quote:
Originally Posted by TheShaman View Post
Guess what opamps are used inside the Metric Halo ULN/LIO-8 "soundcards", to many the most transparent sounding pro-audio interfaces they ever got their hands on.
I see more votes for flat mic-pre to DSP RIAA among its users, many converts from some high-end analog pre-amps.
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Old 21st January 2012, 02:21 PM   #1214
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Yeap, that too.
And they use ye olde NE5532 in there...

Click the image to open in full size.

Last edited by TheShaman; 21st January 2012 at 02:28 PM.
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Old 21st January 2012, 02:58 PM   #1215
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Quote:
Originally Posted by TheShaman View Post
Yeap, that too.
And they use ye olde NE5532 in there...
Cool, that might explain why they recommend a transformer for MC. I guess everything really does sound the same. Does this sound $4500 better than that Behringer?
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Last edited by scott wurcer; 21st January 2012 at 03:00 PM.
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Old 21st January 2012, 03:08 PM   #1216
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Quote:
Originally Posted by TheShaman View Post
And they use ye olde NE5532 in there...
And is that an SMPSU I spy in there too? The saving grace I guess is its balanced I/O right? Where do they connect the pin1s - onto the PCB?
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Old 21st January 2012, 04:06 PM   #1217
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Originally Posted by SY View Post
That's the difference. Never occurred to me to use power. Thanks!
That is because it is wrong; Since it is an audio amplifier I was thinking in percent loudness not voltage ( silly I guess)
as correctly noted:
Signal Power(v) -> 10Log( v^2) = 20Log(v)

I am going to take back my bet on 80db down single spur, see
Sound level SPL to dB - pressure level sound pressure sound intensity - dB conversion of sound units levels calculating spl sound level calculation air sound units level ratio decibel Pa kPa acoustic energy power convert decibels to pascals audio eng
I used this to calculate:
if the there is 33dB(SPL) (.001Pa) signal sitting on audible noise floor; what would corrresponding main harmonic be? I get:

Signal 69 dB(SPL) & 33dB(SPL) noise spur gives a 80dB "single spur" THD.

If I am rocking out at 105 dB ( when I was seventeen I used my Dad's SPL meter to actually measure that on Aerosmith's "Sweet Emotion" through my Kenwood 40Watt integrated amp &12 inch 3 ways, no wonder the Philips tweeters kept smoking.)
I get 3.55 Pa for a .001 Pa noise floor or -117dB down on the audible noise floor, (not sure I remember worrying about a noise floor back in the seventies

"critically loud" say running say 80 dB(SPL) I get -106 dB actually crosses the audible threshold noise floor.
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Old 21st January 2012, 04:10 PM   #1218
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Hi,

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Originally Posted by Wavebourn View Post
Or, go to Siberia during summer, seat on some nice meadow with flowers, look on the water in a lake...
Thank you, but no. These Mozzies are worse than those in West Africa! Probably carry Malaria too (sure killed a lot of Gulag inmates).

Ciao T
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Old 21st January 2012, 04:43 PM   #1219
SY is offline SY  United States
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Quote:
Originally Posted by vanderpol4 View Post
"critically loud" say running say 80 dB(SPL) I get -106 dB actually crosses the audible threshold noise floor.
Not quite- audible threshold assumes that there's no other signal present. Bill Waslo did a brilliant demonstration of that- check out the Listener Challenge on his downloads page:

Audio DiffMaker example files
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Old 21st January 2012, 05:37 PM   #1220
BFNY is offline BFNY  United States
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Quote:
Originally Posted by DF96 View Post
It should be 20 for any voltage measurements,... 0.01% (voltage) distortion is -80dB whether audio, RF or anything else. Guys in that other world use 10 or 20, as appropriate, if they know what they are doing.
Well, I guess my using the word "always" above prompted you. Probably should have stayed with "tend to". When you use transmission lines with 50 or 75 ohm impedance, the predominant units for level are dBm, or dBf, dB referenced to 1 milliwatt, or 1 femtowatt respectively. Clearly, when speaking about watts, this is power. When looking at most RF/Microwave Spectrum Analyzer displays (frequency vs amplitude), the amplitude units to the left will usually be dBm as well.

In audio measurements, we don't worry about standing waves, hence usually no 50 ohm transmission lines, and the most commonly used display on a frequency domain plot (via FFT) is dBV.
So yes, one needs to be careful, as it should be clear, -80 dBm "spurs" or "harmonics" does not mean the same ratio as -80 dBV.

The confusion over sound pressure level (SPL) dB units seem to really get the party going. These dB SPL ratio units should be calculated 20 log (ratio) . I can post links to my Bruel and Kjaer acoustics book scans where this is derived and explained, if people want to see it.

Last edited by BFNY; 21st January 2012 at 05:41 PM.
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