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Old 14th August 2014, 12:25 PM   #51
adason is offline adason  United States
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thanks Davey, that helps
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Old 14th August 2014, 11:52 PM   #52
Davey is offline Davey  United States
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Yeah, initially the meters in some of the plugins indicated incorrectly, as noted by George, but that's been fixed a long time ago.

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Old 19th August 2014, 12:32 PM   #53
gpapag is offline gpapag  Greece
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All the 2x4 plug-ins issued before Mar 2013 where reading –6dB. That was wrong. My posts up to #21 were referring to these plug-ins

After March 12, 2013 plug-ins were revised to correctly read 0 dB with full input signal as Dave wrote. My posts past #24 refer to the corrected plug-ins

George
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Old 19th August 2014, 03:02 PM   #54
adason is offline adason  United States
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Thanks George and Davey for information.
The reason why I am asking about this is that while playing with minidsp, even when I had no eq, flat fr respose, both in and out (digital) volume setting up, no pot volume enabled, and RMS meters do not reach all the way up to 0 dB, I still have the feeling of clipping happening in input ADC.
The reason may be that RMS meter responds poorly to dynamic music signal. Its kind of sluggish. What I would like to have is simple LED indicator for ADC clipping. It would be great if it can be programmed into plugin...and it shows like little light bulb next to RMS level meter, but thats not my call to make.
If I look at REW level meter, its much faster, better behaving, plus besides the normal bar it has that red line indicating the absolute top of the signal. And as you noticed, that is always 5-10 dB higher than the bar. We all know that. But to avoid clipping, I need something which will flash instantly the signal reaches full scale on ADC or DAC.
Those RMS meters in minidsp are just not cutting it.
So my plan is to do simple 2-transistor clipping indicators on the input and output analog signal. That's it. Under no cirumstances I want those to clip.
Long time ago I made such "clipping" indicators on VU meters on every reel to reel I had. Since those mechanical VU meters were responding who knows what, it was nice to know when signal reached 0 dB. It was fun to watch. In very dynamic music, drum solo...VU meter barely moved -30 to -20 dB, yet the LED flashed 0 dB. On other occassions VU meter overshot to +dB, yet the LED for clipping was not flashing...but this if of topic.
While its summer, I have limited time for minidsp now, but eventually I will get to it. I will report back if it works. Thanks, ed

Last edited by adason; 19th August 2014 at 03:05 PM.
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Old 19th August 2014, 05:25 PM   #55
Davey is offline Davey  United States
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An LED clipping indicator would be handy.....both in the plugin and also if implemented externally. However, the tricky thing with a hardware indicator is to get the LED to hold for just the right amount of time. It's actually more challenging (at least for me) than you might think.

I tend to think that this clipping concern is best handled with some beforehand confirmational testing vice observational gadgets. In most cases your maximum source level would be known and the maximum input level of the miniDSP is also known. That makes it easy to fabricate an appropriate attenuator to positively prevent clipping in all cases. OTOH, I understand the large recorded range of program material complicates the situation. Much depends upon where the system volume control is located.

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Old 22nd August 2014, 11:48 PM   #56
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by adason View Post
It was fun to watch. In very dynamic music, drum solo...VU meter barely moved -30 to -20 dB, yet the LED flashed 0 dB.
Adason
You may like to read post #26

And if a software implementation of a real peak meter with with appropriate ballistics and an “over” indicator suits you, here is a source:
Audio Level Meter

Quote:
On other occassions VU meter overshot to +dB, yet the LED for clipping was not flashing...but this if of topic.
That too was due to inadequate control of the needle momentum. VU meter stds were specifying that parameter too.

George
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Old 23rd August 2014, 05:15 PM   #57
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Quote:
Originally Posted by adason View Post
Thanks George and Davey for information.
The reason why I am asking about this is that while playing with minidsp, even when I had no eq, flat fr respose, both in and out (digital) volume setting up, no pot volume enabled, and RMS meters do not reach all the way up to 0 dB, I still have the feeling of clipping happening in input ADC.
The reason may be that RMS meter responds poorly to dynamic music signal. Its kind of sluggish. What I would like to have is simple LED indicator for ADC clipping. It would be great if it can be programmed into plugin...and it shows like little light bulb next to RMS level meter, but thats not my call to make.
If I look at REW level meter, its much faster, better behaving, plus besides the normal bar it has that red line indicating the absolute top of the signal. And as you noticed, that is always 5-10 dB higher than the bar. We all know that. But to avoid clipping, I need something which will flash instantly the signal reaches full scale on ADC or DAC.
Those RMS meters in minidsp are just not cutting it.
So my plan is to do simple 2-transistor clipping indicators on the input and output analog signal. That's it. Under no cirumstances I want those to clip.
Long time ago I made such "clipping" indicators on VU meters on every reel to reel I had. Since those mechanical VU meters were responding who knows what, it was nice to know when signal reached 0 dB. It was fun to watch. In very dynamic music, drum solo...VU meter barely moved -30 to -20 dB, yet the LED flashed 0 dB. On other occassions VU meter overshot to +dB, yet the LED for clipping was not flashing...but this if of topic.
While its summer, I have limited time for minidsp now, but eventually I will get to it. I will report back if it works. Thanks, ed
I faintly recall reading a post that showed clipping at levels that were below the full output level for the miniDSP, but I can't put my finger on it now. So what you think you are hearing/perceiving may actually be correct.

If you want to build your own clipping indicator, there is a nice project (although its designed to be used with for an amplifier) at Rod Elliot's web site:
Power Amp Clipping Indicator
The essential part is the pulse stretcher. This allows even brief clipping to be made visible with the LED. Since the voltage levels are much lower for line level you may need to implement the diodes as an ideal diode (in feeback of op amp) and make other adjustments, but the basic idea can remain the same.
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Old 23rd August 2014, 10:56 PM   #58
Davey is offline Davey  United States
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Actually, the clipping level is slightly above the advertised full output levels on the miniDSP products. The 2x4 unit, for example, exhibits clipping at approximately 0.95VRMS on both input and output. The 2x8 unit is specified with a 2VRMS output, but it actually outputs 2.5VRMS without clipping.

The only true way to evaluate all this is with an oscilloscope......which I've done on all these units.

I'd forgot about Project 23 on Rod Elliot's site. Thanks for posting.

Cheers,

Dave.
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Old 3rd September 2014, 03:50 AM   #59
adason is offline adason  United States
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Here are two peak indicators i am going to experiment with. I have made the simple two transistor peak level indicator many times in the past, its the circuit i mentioned that i used to build into needle vu meters. I think i am going to put one jfet in front of it to increase input resistance. Otherwise it behaves well.
Second circuit...i have not build yet, so no direct experience.
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Old 6th September 2014, 12:34 AM   #60
adason is offline adason  United States
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I am not sure this is too helpful, most likely just a repeat of what others said, but anyway, this is what I got on the output of minidsp when 1kHz sine wave signal of various intensity was measured on the output by small digital hand held oscilloscope (I know maybe not too accurate) in comparison what the output level meter is showing...

at 0.7V rms level meter shows -10.5 dB
at 0.8V it shows -8.3 dB
at 0.9V it shows -6.1 dB
at 0.93V it shows -5.4 dB and clipping occurs (and is audible)
at 0.94V it shows -4.9 dB and severe very audible clipping happens

This may not be too precise, but this is what I got...

Last edited by adason; 6th September 2014 at 12:37 AM.
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