Hey Jens... 1). Don't call it VU unless you match the actual ballistics of the ORIGINAL VU meter
2). Europe tends to use a PPM [quasi-peak] system. Peak Program Meter. 3). Consumer and pro levels are very different. They are often misunderstood and hence mounds of garbage appear on the web. 4). dB is a ratio and a reference must be stated. Thus you must choose what reference your 0VU is. 5). Your headphone out MIGHT be the Line Out. There are [quite a few] standards for Line Level. 6]. A useful fact relates to the maximum level that can be digitally encoded. A CD can produce a certain maximum digital value. That gets converted to some analogue value. You can work empirically by using [say] standard test tones from the web OR an audio program like Audacity to produce known digital levels. 0 dBFS is the max level... BUT there can be output results higher than this [long topic], so work on using either -0.3dB or even -3dB below (or do I mean over? Semantics ) this as maximum. 7). In "recent" years the "loudness wars" and misuse of Digital Audio Workstations has resulted in CDs and digital audio having bugger-all dynamic range. Magnetic tape was automatically a limiter [curved]. People using digital should be working [say]20dB down from max.... but the signal level looks so tiny to them in "oscilloscope" mode. They think that they are getting better results by working "hot" and getting the best sig/noise ratios. Their loss of dynamic range is not a good outcome. I mention this because it DOES relate to the choice of 0 dB[ref]. BTW.. some digital audio actually clips! The master has too much dynamic range for the "cutting" [vinyl, cd , web etc] engineer. He wants it to sound HOTTER. Sigh. 8). Talking the voltage levels. The term dBU refers to a bridging voltage measurement. These days you definitely do NOT want to try expecting 600 ohm impedances. The "usual" outputs are these days exceptionally low... eg way under 20 ohms. This way you can feed a great number of inputs from one output. Big topic. The problems start here for your question. Many consumer outputs place a series resistor for protection purposes. This doesn't affect Bridging (high Z meter) readings much, BUT the input impedance of the loads does. And the number of such loads connected. There are many manufacturers who conform to certain industry standards, and many more who don't. 9). Read Bob Katz book Mastering Audio. Downloadable, although I didn't check which editions. I use 2nd edit for recording because I do not do web stuff. His later edition(s) cover the "modern" approach. [read Amateur Fiddling for modern :-)) ] 10). I suspect that the most useful meter for your purposes is one which relates well to the maximum signal level and has fast response. BUT VU is so averaged and hence slow. There are many so-called VU that are fast reacting and hence display peaks. And be careful of the definitions here when you see rms stated. As David said, work with peak voltages that you can see on a scope. This is where you need to start looking at the Orban meters. I haven't checked but they were downloadable. Apart from the damping factor for Peak, his special meters that relate to perception are interesting. He covers the standards for TV advertising versus program content. And that leads to discussions of loudness [not volume]. Reminder... VU can ONLY be used when the meter has the defined ballistics. See the BTSJ papers from the 1940s iirc. And the original meter HAD/HAS to have the attenuator incorporated. The use of the meter without recognising the lack of sensitivity led to the actual zero level of +4dBm. The original switched attenuator had zero attenuation in the 4 position. It takes +4dBm to drive the meter to the zero indication. Big topic too. Watch out for web misinformation. You can check my version by referring to the papers. I can not [easily] access all my digital archives at present so I am not providing full details. 11). As David implied... I think you will need a sensitivity adjustment. Users can calibrate the zero to represent whatever they want. The meter characteristic/ballistic HAS to be known by a serious user. There are examples on the web. Whatever you do has to provide for the whole audio chain.. there has to be headroom everywhere so that there is no clipping. 12). Here is a typical online statement - this one form Audio Technica :- "Line level refers to the typical level (strength or amplitude) of the audio signal from mixers, signal-processing equipment and other consumer and professional audio gear. There are two line level types: consumer and professional. Consumer line level is generally thought of as a signal whose level is at -10 dBV (0.316). CD players and DVD players are examples of consumer line level equipment. Professional line level is generally thought of as a signal whose level is at +4 dBu (1.23 volts or significantly higher). Signal-processing equipment and professional mixing consoles are examples of professional line level equipment." Done quickly, apologies for errors and omissions, John Kaesehagen Australia -----Original Message----- From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On Behalf Of jb-electronics Sent: Thursday, 28 March 2019 11:42 To: neonixie-l@googlegroups.com Subject: [neonixie-l] OT: audio levels Hello Nixie friends, I am thinking of building a simple all-in-one VU meter using a microcontroller to visualize the audio signal on a headphone line (say, I feed the headphone output of my PC to my circuit, and then I install a pass-thru to connect to my headphones). What is the typical voltage amplitude I should expect? I do realize this question is quite general, but perhaps you can point me in the right direction? Many thanks! Best wishes Jens -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/2a4dfbef-7430-06ac-b272-973d84c6dae8%40jb-electronics.de. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/000801d4e56f%24f21ca0c0%24d655e240%24%40internode.on.net. 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