[LAD] A little quiz about audio measurements...

[Ralf Mardorf]

Gene Heskett wrote:
> On Friday 28 May 2010, fons at kokkinizita.net wrote:
>   
>> On Fri, May 28, 2010 at 11:24:29PM +0200, Ralf Mardorf wrote:
>>     
>>> Oberhausen, Rheinland, Germany; power line frequency right now is at
>>> 49 Hz, measured with a low cost energy consumption costs meter.
>>> Those low cost meters shouldn't be able to do correct measurements
>>> ;). The best test at home might be to compare the sound of a
>>> transformer with a 50 Hz sine wave.
>>>       
>> 49 Hz is impossible. It would mean that a clock using this
>> frequency would be slow by more than a minute per hour.
>>
>> Long-term accuracy is extremely high, precisely because clocks
>> depend on it. And since almost all of Europe is interconnected,
>> adjusting the frequency must be a _very_ slow process. So errors
>> of 2 percent really can't be tolerated.
>>
>> Ciao,
>>
>>     
> [snip]
>
> Yup, broadcast engineering can be a "but that can't happen (but it just 
> did)" scenario at least once a week.
> [snip]
>   

Full ACK :D. I once repaired a mic cable. The so called 'audio engineer' 
who 'repaired' it before I did it, didn't know what a 'balanced' 
connection is, he thought 2 cords and 1 shield must be a stereo cable 
for a stereo mic. What he wanted was a connection that fit the mono 
microphone to a 6.3 mm stereo jack for a consumer cassette recorder. 
O'Toole's Corollary of Finagle's Law: 'The perversity of the Universe 
tends towards a maximum.'

Veronica Merryfield wrote:
> On 2010-05-28, at 3:26 PM, fons at kokkinizita.net wrote:
>
>   
>> [snip]
>>     
>
> Assume it at your peril. The usual spec is to arrange that over a given 24 hour period, the total cycle count will result in a mains clock being within 1 second. Often, the power generators can get much closer and I believe these days they use atomic clocks as the reference 24 hour time period.
>
> The frequency will drop upon sudden demand. This is often coincident with the start of adverts in a national sporting event or high ratings soap, end of the news broadcast and so on. It takes a while to add more power and as a consequence the rotating machines will slow. Also, things like storm damage removing a significant section from the grid will result in an increase in frequency. 
>
> Vrnc

I don't think that we need to worry too much about the frequency. In the 
morning, when all the people turn on all the coffee machines and 
toasters, might be a bad time to adjust the H/V deflection for a 
television set, because of the voltage that differs, but the frequency 
should be stable. But indeed, during a snow storm the frequency will 
drop extremely, but if so, we will hear about power blackouts in the 
radio news, this happened e.g. in 2006 in Western Europe, there we had 
around 49 HZ.

I guess even if it's OT, it's important. We won't a Hammond B3 become 
similar to a tuning unstable Minimoog.

Indeed Veronica and Gene, I guess Fons is right. Yesterday evening it 
wasn't 49 Hz, but a bad measurement done by my supermarket meter. But 
who knows? Maybe the frequency really was down. Regarding to station 
clocks I guess they are synced by radio and not by the power line. In 
Parma there the clocks might be heritage-protected ;) and stills synced 
by the power line frequency.

Cheers!

Ralf

-- 
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