[ProAudio] VU meter permitted overdrive with a sine wave...

Richard L. Hess lists at richardhess.com
Fri Jan 29 08:49:35 PST 2021

Hi,  Jay,

The language I posted from the IRE 1954 publication says ***five*** 
times for continuous overload. Where did your "three times" wording come 

The 1940 Chinn article you link to states, "5. Overload The instrument 
is  capable of withstanding, without injury or effect on calibration, 
peaks of 10 times the voltage  equivalent to a deflection to the 0-vu or 
100 mark for 0.5 second and a continuous overload of 5 times the same 
voltage." (cut and pasted from the link in your message).

What triggered me to look was I had said "+20 VU and +14 VU," while you 
said "+20 dB and +10 dB," so I wanted to make certain one of us hadn't 
made a silly math mistake. We hadn't. We had different versions of the text.

Another discrepancy: The text I cited did not provide specific times, 
but said "momentary" and "continuous." The quote from the Chinn paper is 
"0.5 second" while the quote you posted below is "5 s."

We need someone to say, "The nice things about standards is we have so 
many!" Oh, I just did!

One minor nit. The VU is relative to reference level and as measured on 
a VU meter. Therefore, I think it is less ambiguous to make it clearly 
relate to the reference level as shown on the meter, one should use "VU" 
rather than "dB." In the common common practice today with 0 VU = +4 
dBu, that would be +24 dBu for 5 s (or 0.5 s) and either +18 dBu or +14 
dBu (five or three times the overload) continuously. Of course, back in 
1954, 0 VU was most often +8 dBm, so different levels would prevail.



On 2021-01-28 10:15 p.m., Jay at MRL Support via ProAudio wrote:
> Re: [ProAudio] VU meter permitted overdrive with a sine wave... Hello Bob,
> It appears that no-one has ever read any of the once-published 
> standards on the vu meter.
> "15 Overload input level - Performance requirement
> "The indicator shall withstand, without damage or any effect on 
> calibration,
> an overload of ten times the voltage giving reference indication for a 
> time
> interval of 5 s and an overload of three times that voltage for unlimited
> period of time. "
> That would be +20 dB and +10 dB, respectively
> This same text is in the original Chinn IRE ~1940 paper ( 
> https://www.aes.org/aeshc/pdf/chinn_a-new-svi.pdf 
> <https://www.aes.org/aeshc/pdf/chinn_a-new-svi.pdf> ), the IRE 
> Standard, the IEEE Standard, the ANSI Standard, or the current 
> Standard, IEC 268-17.
> On Thursday, January 28, 2021 at 9:26, you (Bob Katz via ProAudio) wrote:
> 	This list has been remarkably silent, but I am very grateful that 
> it's around when I have a question to ask AUDIO EXPERTS.
> Who here knows the acceptable rating of a standard mechanical VU meter 
> above 0 VU with a sine wave?  If I recall correctly, they are designed 
> to accept as high as +6 VU or even higher. For example, when doing 
> testing of a tape recorder for headroom. It's still ideal to shut off 
> the meter, but in some cases that's not possible.
> Thanks and happy New Year!
> Bob
> -- 
> /--
> Best regards,
> Jay McKnight
> at
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Richard L. Hess                   email: richard at richardhess.com
Aurora, Ontario, Canada           http://www.richardhess.com/
Quality tape transfers -- even from hard-to-play tapes.

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