Hello,
This is my first question although I have been browsing this forum for a long time.
I'm working on a design of a Peak Level Detector in combination with a VU Meter. The VU meter works great, It is proven to be working as intended. The 0dBu is set at 0,775Vrms with a 1kHz sine.
As 'peak' level +3dBu is set with this 1kHz sinus testsignal. When adjusting the Peak Level Detector to +3dBu, the LED turns on. At 0dBu the LED turns off. So it seems the design is working.
When using with music however, I noticed that the LED turns on much earlier than +3dBu. The LED starts to turn on at around -6dBu. The VU meters are working as intended. When checking with a recorded testsignal (1Khz/sinus), and parts of music on the same tape, the VU meter and the Peak work as intended at the part of the testsignal. When music is played the problem is again visible. It seems that with a complex (music)signal the Peak Level Detector turns on to early. Tests have been conducted with a 1Khz square, sawtooth and a triangle. And results ar roughly the same. LED turns on at +3dBu. It depends a little on the type of music is played but in general only with music the LED turns on to early.
I wonder has this to do with the Crest factor? What kind of signal and/or level of testsignal will adjust the Peak detector at the desired +3dBu correctly?
Regards,
Nev
This is my first question although I have been browsing this forum for a long time.
I'm working on a design of a Peak Level Detector in combination with a VU Meter. The VU meter works great, It is proven to be working as intended. The 0dBu is set at 0,775Vrms with a 1kHz sine.
As 'peak' level +3dBu is set with this 1kHz sinus testsignal. When adjusting the Peak Level Detector to +3dBu, the LED turns on. At 0dBu the LED turns off. So it seems the design is working.
When using with music however, I noticed that the LED turns on much earlier than +3dBu. The LED starts to turn on at around -6dBu. The VU meters are working as intended. When checking with a recorded testsignal (1Khz/sinus), and parts of music on the same tape, the VU meter and the Peak work as intended at the part of the testsignal. When music is played the problem is again visible. It seems that with a complex (music)signal the Peak Level Detector turns on to early. Tests have been conducted with a 1Khz square, sawtooth and a triangle. And results ar roughly the same. LED turns on at +3dBu. It depends a little on the type of music is played but in general only with music the LED turns on to early.
I wonder has this to do with the Crest factor? What kind of signal and/or level of testsignal will adjust the Peak detector at the desired +3dBu correctly?
Regards,
Nev
A True VU meter is slow and approximate. A Neon/LED peaker can be quick and exact.
The lead factor, headroom, between peak and VU runs 10dB to 18dB.
AM radio is traditionally worked 10dB because S/N is precious and live radio distortion is short and one-time. AM console level was traditionally re: +8dBm and the amps needed more than +18dBm "clean".
Studio practice tends to 18dB, because they run the same sections over and over and the clips become annoying. Studio level is traditionally +4dBm so right away we have 14dB headroom; "good" recording gear went +20 or +22dBm so 16dB or 18dB headroom.
You have to ask what you are doing, what is your goal? In the days of digital, VU meters are more eye-candy than technical monitors. They do have some use for "loudness" (they were designed for that) but Dorrough meters do it better, and most DAW software has loudness algorithms.
If you just want to keep a power amp out of clipping, all you need is peaks.
The lead factor, headroom, between peak and VU runs 10dB to 18dB.
AM radio is traditionally worked 10dB because S/N is precious and live radio distortion is short and one-time. AM console level was traditionally re: +8dBm and the amps needed more than +18dBm "clean".
Studio practice tends to 18dB, because they run the same sections over and over and the clips become annoying. Studio level is traditionally +4dBm so right away we have 14dB headroom; "good" recording gear went +20 or +22dBm so 16dB or 18dB headroom.
You have to ask what you are doing, what is your goal? In the days of digital, VU meters are more eye-candy than technical monitors. They do have some use for "loudness" (they were designed for that) but Dorrough meters do it better, and most DAW software has loudness algorithms.
If you just want to keep a power amp out of clipping, all you need is peaks.
What you are seeing is the crest factor of music. Music average level is much lower than its peak level. The calibration is accurate since a Sinewave has a peak voltage of 1.4X its RMS voltage. Music can easily run 10X peak to average (unless its heavily compressed like a radio station.)
So, it seems the effect I see is indeed the Crest factor. Check ...
Second part of the question was what kind of signal and/or level of testsignal will adjust the peak detector at the desired level. Like I mentioned I have tried a square signal (CF=1) but no changes. Is there some kind of signal/level known to somebody in this forum?
Second part of the question was what kind of signal and/or level of testsignal will adjust the peak detector at the desired level. Like I mentioned I have tried a square signal (CF=1) but no changes. Is there some kind of signal/level known to somebody in this forum?
What do you want to know from the metering? Different applications have different requirements. Audio level monitoring on program is almost more art than science. At the same time peak level is important to be sure you are not overloading/clipping. A sine wave is the most unambiguous way to set everything since its values are well known. A square wave will be be pretty unpredictable depending on frequency, rise time etc.
It seems that the answer is "no signal/level does exist". So how do you people adjust the peak level? Just by trying?
You have not given the least clue to what you are metering. For disc? For tape? For ADC digital recorder? For monitoring and equalizing long transmission lines? Power amplifier level? For nuisance loudness monitoring? For eye-candy?
If you want to show the true peak voltage level then the detector should operate at 3dB higher than a steady state RMS sinewave signal . Alternatively if you just want the peak detector to indicate when the VU meter would register +3db using a steady state sine wave signal then you adjusted it correctly in the first post . PRR was pointing out that VU meters are inherently slow to respond and the peak detector is showing you this , they give a general indication of volume , whilst peak program meters ( PPM ) were developed to show the actual voltage peaks ( or very nearly ) . PPM and VU meters have quite different specs .
Yes, each indicates something else.
I once had rtr with needle vu meeter, with built in +3dB led in the corner. It was fun to watch how much vu and peak differed, especially needle vu.
Depending on music.
For instance when all the symphony orchestra started at once and hold, needle could swing violently to the end of scale, yet led would not lid up, since the signal did not reach over 0dB.
In techno with short transients vu needle was down low barely moving, yet let was blinking.
Fun.
Best is fluorescence meter with vu bar and peak spot staying for a second ot two.
I once had rtr with needle vu meeter, with built in +3dB led in the corner. It was fun to watch how much vu and peak differed, especially needle vu.
Depending on music.
For instance when all the symphony orchestra started at once and hold, needle could swing violently to the end of scale, yet led would not lid up, since the signal did not reach over 0dB.
In techno with short transients vu needle was down low barely moving, yet let was blinking.
Fun.
Best is fluorescence meter with vu bar and peak spot staying for a second ot two.