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Old 26th April 2003, 05:39 PM   #11
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Default Maybe this is what you wanted.....

I usually shoot for 0.5 V rms, using the standard 5 cm/sec 1 Khz test tone.

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Old 28th June 2003, 11:40 PM   #12
PGW is offline PGW  United States
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Quote:
I usually shoot for 0.5 V rms, using the standard 5 cm/sec 1 Khz test tone.
Sounds reasonable...

or 0 dBU = 776 mV rms (into 600 Ohms, for the purists).
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Old 29th June 2003, 06:52 AM   #13
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Default If we're going to be pure about it...

0dBu = 775mV RMS and is the voltage that would have dissipated 1mW in a 600R load, but it does not specify an impedance.

0dBm = 1mW into 600R. But this is virtually impossible to measure (most meters calibrated dBm actually measured dBu).
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Old 29th June 2003, 09:16 AM   #14
AuroraB is offline AuroraB  Norway
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Talking Just to mess everything up..

And there is also the the 0dbV = 1V, as used by a lot of studio equipment of today...this one also being impedance independant.
The 600 ohms nominal load seems to mostly for measurements and calibration purposes.

Most units today will be rated around 1V sensitivity, or contrary, output level. This is of course not the same as clipping level, which is design dependant.
Older units, like cassette decks of european origin, often had 100-200 mV as nominal output level, whereas the japanese were among the first to somewhat standardise 1V, or thereabouts..
Cirka thereabout is probably the closest we can get....

CDs vary quite a lot, in terms of max output, or full scale level, and this is both the actaul discs themselves as much as the players we use. Personally, I cannot recall ever having seen a calibration level for CDs...??? Anyone else??
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Old 29th June 2003, 09:29 AM   #15
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600R is historical, and comes from the days when wires strung on telegraph poles had a measured characteristic impedance of 600R. Before anyone starts wittering about transmission lines and audio, I must emphasise that for transmission lin effects to become noticeable, the cable length has to be a reasonable proportion of one wavelength. In audio terms, that means miles, not metres.

The specification for CD players is that a maximum amplitude sine wave (using all possible bits) should produce 2V RMS. Early CDs didn't use all the bits because of metering problems during mastering.

Modern CDs are recorded at greater resolution, then tweaked so that they just avoid 16 bit digital clipping. Also, the CTF control is turned right up. (Compressed To F^*&)
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Old 29th June 2003, 10:33 AM   #16
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Default In the RF world.....

0 dBm is 1 mW into a 50 ohm load........0.224 V rms.

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Old 29th June 2003, 05:14 PM   #17
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Default And for complete confusion...

Thank goodness we hardly use dBs for video. There, we have 1V pk-pk into 75R.
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Old 30th June 2003, 07:02 AM   #18
AuroraB is offline AuroraB  Norway
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and dBuV for R/TV signal strength........
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Old 3rd July 2003, 07:08 AM   #19
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Quote:
0 dBm is 1 mW into a 50 ohm load........0.224 V rms.
This is not a correct definition of dBm, 0 dBm means a power level in dB relative to a reference power of 1 mW U]regardless[/U] of impedance.

So for 50 ohm 0dBm is 1mW = 0.224 V RMS measured over the load.

and for 600 ohm 0 dBm is still 1mW but 0.775V RMS measured over the load.

Regards Hans
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Old 3rd July 2003, 03:15 PM   #20
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Didn't I say "in the RF world"???????????

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