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Guru of Grounding
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re: 2 Vrms - A funny old standard
Guru of Grounding   9/4/2009 11:18:21 PM
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I'm late to this thread, but I have 2 comments: 1. Mr. Roche says "Traditional interface standards were given at +4 dBu and -10 dBV. For many years, this was what differentiated consumer and professional equipment." In fact, the most important difference between consumer and pro interfaces is that the consumer interface is unbalanced (with its inherent common-impedance noise coupling problems) and the professional interface is balanced (which can, if properly implemented (another pet peeve of mine), reject noise due to driver-receiver ground voltage differences). 2. On the subject of "proper" balanced input stages, the example in Figure 50 of the TI data sheet for the PCM4222 is a prime example of a circuit that will produce truly awful CMRR when connected to real-world equipment because its common-mode input impedances are far, far too low! I've published several AES papers on the subject ... but they never seem to reach the folks that need to know. I'll happily send copies to anyone interested - e-mail me at whitlock@jensen-transformers.com. Bill Whitlock, President & Chief Engineer Jensen Transformers, Inc. AES Life Fellow, IEEE Senior Member

searing
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re: 2 Vrms - A funny old standard
searing   8/28/2009 4:46:23 PM
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Another disadvantage to Solution #2 is the potential for microphonic problems. All three capacitors (C1, C2 and C3) have a voltage bias, and therefore if Class 2 or 3 ceramic capacitors (Y5V are the worst I've run into) are used, microphonics (at some level) would be expected. The microphonic noise pickup may be low, but there are other issues with capacitors that affect the sound quality.

Ruth123
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re: 2 Vrms - A funny old standard
Ruth123   12/4/2008 8:54:58 AM
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lily2008110
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re: 2 Vrms - A funny old standard
lily2008110   11/26/2008 4:19:13 AM
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The Artful Bodger
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re: 2 Vrms - A funny old standard
The Artful Bodger   10/13/2008 11:01:30 AM
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Hi, > The main thing I would like feedback on, now that you're engaged is discussion regarding this, is what you both think of > directpath technology - the amplifier and the charge pump in the same package etc. From a BOM/COST/Complexity view it seems a great idea. I am not sure how good it is to have on-chip an chargepump with a frequency quite close to the audio band and with frequencies that can couple nicely. If all the problems (potential or real) inherent to having these things on chip can be fully solved, it would be rather neat. And an option for 7.75V RMS full scale balanced "pseudo transformer" inputs and outputs that can run directly of a single 5V supply at low cost would amke a lot of studio gear manufacturers quite happy....

Godwins
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re: 2 Vrms - A funny old standard
Godwins   10/11/2008 10:19:09 AM
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The Artful Bodger
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re: 2 Vrms - A funny old standard
The Artful Bodger   9/6/2008 6:29:27 AM
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Actually, first, the 2VRMS standard for 0dbfs came in with the very first commercial CD-Player (the Philips CD-100 see technical data @ http://www.marantzphilips.nl/index.asp?strPage=Info&strBrand=Philips&strType=Philips_cd100). So looking at an old (or current) HiFi CD-player will always reveal 2VRMS @ 0dbfs excepting a tiny minority of cases. As most traditional analog system allowed as much as 15db headroom above the notional 0db point; 2VRMS @ 0dbfs is actually close to around -10dbV with 15db headroom, when translated back into traditional analog systems numerology. (For example LP, 0db is set as 5cm/s but maximum levels are standardised as 25cm/s or +15db; I cannot now readily remember the old modulation index of FM radio for "0db" but it was way below 100% too and open reel tape allowed at least 10db headroom in the 300Hz - 3Khz region, leading to many recording engineers running tape machines with the VU Meters [hence virtually useless meters] pegged most of the time at louder passages) This then is the ultimate source of the 2Vrms standard, it was set as nearest full value at least 15db above 0db consumer standard (around 0.3V/-10dbV) of the time, so loudness levels would be comparable. The loudness race starting in the late 80's and continuing up to today has shifted the average level on CD (and other digital recordings) progressively upwards from the -15dbfs baseline at the cost of ever more reduced crest factors and musical realism. But that as they say is another story. Basically a kind of "around 1-2Vrms @ maximum modulation" standard was already implicit in old analog media 0.3V @0dbvu due to headroom requirements and was formally codified with the arrival CD, removing any headroom consideration (which may vary depending on medium) from the equation. Non of this makes ay of the challenges to fulfill the necessary requirements any less interesting though. Even more interesting are the now common requirements in pro-audio equipment of presenting levels of +20dbu (7.75V RMS!) for 0dbfs. This is an area where line drivers with build in stepup from 5V DC (USB bus power) to +/- 15V internally could help majorly reducing BOM items and costs.

EricStromberg
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re: 2 Vrms - A funny old standard
EricStromberg   9/5/2008 3:39:30 PM
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Actually, the traditional standards are +4 and -20. -10 didn't come along until the MIDI keyboards of the early 80's.



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