Modifying QPPM to measure "Max. True Peak Level"

[audiomixer]

alex,

you can calibrate your meters gain to display full scale at -6.81241237 dBu - this is equivalent to 1V PP set this as a reference for your dBpeak and you will read dBpeak values on your meter. of yourse 1v pp is arbitrary, but now you have your reference value to peak. feed a sine wave of precisely -6.81241237 dBu and adjust the gain so that it just peaks. you might need a adjustable gain stage to get the exact value...

of course you can adjust for any other V pp as per your own taste - calculations here:
http://www.sengpielaudio.com/calculator-db-volt.htm

- hope you will find this helpful, happy modding

- cheers,

michael

 

[abbey road d enfer]

Do I just have to feed it with a 1Khz sine, and calibrate?

Yes. If the trimmer has enough range. If not, you can use a 3dB buffer in front of the meter...

"Long strange journey" is maybe your opinion - if there were some more technicians arround,

Very arrogant. You don't realize you have the benefit of some of the best audio designers in the world, ready to answer your questions. It's only your stubbornness and lack of structured presentation that have made things difficult.

I deliberatly asked in a very general way, because I searched for a more general answer that can be referd to the most peak meters.

You can't expect a generic answer because different manufacturers have different ways of presenting and implementing their paradigms.

My opinion is, that eventually there are some people arround, who are really interested in this topic, because the advantage of this application would be, to measure true peaks, if we combine the "TPPM" with a DAC. In my backround of usage, this "TPPM" is just for fun, to see how it would perform.

Honestly, the subject is somewhat boring, because it has no practical consequences. What can you do if you hit an over? Too late...
that's what headroom is for. Interesting for metrology specialists though.

 

[JohnRoberts]

Just digital signal processing Theres still the problem of eliminating the RMS-factor!

For one thing, DSP is over kill for a meter... The last meter I designed used a simple RISC microprocessor.

I remain confused, not about meters which i have designed over several decades, but about what you are asking for.

RMS, implies an integration time (square root of integral sum of values squared) so there is little meaning in "instantaneous RMS". I actually coded a RMS algorithm for my last digital Peak/VU meter (for the slow VU display), but discarded it because the appearance was more dominated by the time constants used than the RMS vs. simple average computation, so not worth the added complexity IMO. (While no doubt it has value to marketers, and customer perception).

I cant take any pictures of my PPM at the moment, and I think if the signal processing is done digitally, hacking it is not easy.
But a friend of mine has a 277-400, maybe this device works totally with analog-circuits.
If I can identify some trim-potentiometers, how can I change the setting to get 29% more on the bargraph?
Do I just have to feed it with a 1Khz sine, and calibrate?

Like I mentioned several posts ago, just turn up your feed to the meter 3dB.

"Long strange journey" is maybe your opinion - if there were some more technicians arround, and if there hadnt been the same questions again and again, this journey wouldnt have been so long.

I haven't been a technician since the '70s, but I have designed meters both using analog and digital technology (including 2 US patents about meters). So I am both interested and know a little about it. While i don't know details about every meter ever made.

I still don't have a clear understanding of what you are asking for. Veers have ranged off on tangents including "loudness", "between digital sample peaks", PPM attack times, simple level calibration, etc.

I deliberatly asked in a very general way, because I searched for a more general answer that can be referd to the most peak meters. Of course I understand that this wish cant be combined on the one hand with totally analog devices and on the other hand with semi-digital processing.

once again huh?

With digital technology meters you can add all kinds of situation specific display features, but i won't go there either.

This brings me back to what is the purpose of a meter. I see two dominant functions. 1) determine signal headroom before clipping the audio path, 2) relative or approximate loudness. 

My opinion is, that eventually there are some people arround, who are really interested in this topic, because the advantage of this application would be, to measure true peaks, if we combine the "TPPM" with a DAC. In my backround of usage, this "TPPM" is just for fun, to see how it would perform.

Glad at least one of us is having fun...

JR

 

[audiomixer]

JR , I think this must be a cultural misunderstanding, not a technical thing ;-)

- michael

 

[1954U1]

Slightly OT..
Only to give a big thanks to you experienced people here..
Its amazing the amount of valueable infos and learning help one can found in this place.