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Old 21st May 2013, 09:44 PM   #41
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hello from france.
thanks to gpapag and minidsp team for this upgrade,
meters are more realist now.
Click the image to open in full size.

question for "minidsp team": is it possible to increase the out delay time?
7.5ms on 2X4 balanced, it's enough to align drivers in a enclosure but not enough to align delays line in a multi diffusion application.
there is the same pb with the 8X8 ( 15ms in analog, 8ms in digital).
the minisharck can grow to 3000ms!
thank's for all.
best regards
manu.
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Old 6th November 2013, 03:41 AM   #42
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Hi George-

First, thank you for all of your work on this. This is without a doubt the best thread I've come across RE: the mini-dsp and input signal clipping.

We communicated a bit via PM but I think as you mentioned the forum will benefit from what we can discuss here.

I'm curious to know what the options are for a mini-dsp user who has an AVR that puts out voltage high enough to clip the mini-dsp inputs.

This is strictly for the sub out line. I'm using an AVR> balanced mini-dsp, with the input jumper set to 2.0 volts> pro-audio amp that requires 2.25 volts to drive to full power.

For whatever reason, even though it's speced at a max out of 2.0 volts my mini-dsp puts out at least 4.8 volts on the meter. (oh wait.... don't they calculate that part of their specs in a different way? like dbu or something?) So confusing...... anyways it powers my pro amp fine.

The problem is on the input side.

I had asked you in PM and you said one could put an attenuator on the pre-amp out of the AVR line that has too high of voltage.

Can you elaborate a bit on why one would do that instead of just turning down the inputs on the mini-dsp? I believe it has to do with the fact that turning down the inputs wouldn't help the problem because the input attenuators do their job after the ADC. Same for the output side. Is that correct???

Another way that might work (would like your input) is-

One can set the max listening level lower on the AVR. E.g a -10 vs. the AVR default of 0, when calibrating all the front/center/left/surround/sub channels. This would lower the voltage at max listening level by however much the AVR does so at a reduction of 10db.

In my example (to give you something to work with here)....at max listening volume on AVR before clipping, after setting the gain structure, I have ~ 4.5db of headroom on the mini-dsp meters while playing a pink noise @ -3dbfs.

If I put on a sub demo track with a high bit rate (mixed rap/jazz/rock) the mini-dsp reaches input signal meter levels of -0.1 and -0.2 which seems like max but it's hard to tell. (Another great point you bring up in this thread- the meter makes it hard to see just how far the signal is maxing out)

FWIW my input jumper is on 2.0 volts. I am aware the .09 setting takes headroom away in a situation like this. ~ 6 db if I remember right.

Also FWIW I'm not running my setup maxed at all. My sub trim is -7 out of 12, and I figure (no scope or mic in for RTA) that my sub out of my AVR starts to clip about 30% of the max voltage at max volume and sub trim. In my case max voltage was 10.6. 30% of that is 7.42 volts. That equals a volume level of 1.5 db on the AVR, but that's with sub trim maxed.

All my mini-dsp tests were done with speakers disconnected, AVR at the 1.5 master volume, and sub trim at +3 (max is +12) which is 10db hot from the standard 75db calibration most AVRs calibrate the system at, including mine.

So you can see I'm not maxed out, far from it.

If I can provide any more info on my setup to help you let me know.

I mostly want to pick your brain about ways to deal with the input of the mini-dsp being clipped.

Look forward to your reply.
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Old 6th November 2013, 06:19 AM   #43
gpapag is offline gpapag  Greece
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Hi pdxrealtor

Quote:
Can you elaborate a bit on why one would do that instead of just turning down the inputs on the mini-dsp? I believe it has to do with the fact that turning down the inputs wouldn't help the problem because the input attenuators do their job after the ADC. Same for the output side. Is that correct???
Yes this is correct.
Please visit again post #5 (read the whole post):
Quote:
Originally Posted by gpapag View Post
The Input attenuation slider is implemented in the digital domain, past the input, after the A/D conversion. So, when a signal applied at the input has an amplitude greater than the clipping threshold level, it overdrives (clips) the A/D converter.
Adjusting the input attenuator to a lower click, will not attenuate the analog input signal that would prohibit the A/D clipping. It will attenuate the digital clipped signal which will be further processed and furnished to the outputs in itís clipped form.


Quote:
In my example (to give you something to work with here)....at max listening volume on AVR before clipping, after setting the gain structure, I have ~ 4.5db of headroom on the mini-dsp meters while playing a pink noise @ -3dbfs.

If I put on a sub demo track with a high bit rate (mixed rap/jazz/rock) the mini-dsp reaches input signal meter levels of -0.1 and -0.2 which seems like max but it's hard to tell.
Again, I would stick to ~20-24db of headroom when testing with noise signal
http://www.meyersound.com/pdf/cinema...ech_report.pdf

Important:I hope that you already have upgraded you miniDSP audio plug-in so that the input RMS meters are reading correctly.


Quote:
Also FWIW I'm not running my setup maxed at all. My sub trim is -7 out of 12, and I figureÖ
From here on on your post, I read conflicting numbers and some high voltage readings. What is going on?
With what instrument do you measure the signal amplitude?
You have to use a sinudoidal signal for to reliably measure the signal amplitude. Donít use pink, white or any noise signal for that.
If you donít have any real meter, use miniDSP input RMS meters but again, use a sinudoidal signal for to reliably monitor the signal level. Read post #25:
Quote:
Originally Posted by gpapag View Post
C. RMS Meter reading with sinusoidal signal
Which is your AVR model?

George
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Old 6th November 2013, 08:17 PM   #44
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[QUOTE=gpapag;3693077]Hi pdxrealtor



Quote:
Yes this is correct.
Please visit again post #5 (read the whole post):
Post 5 is very informative and IMO one of the best posts in this thread. I was not sure, after reading the this thread and ALL of its posts more than once, that some of the information in that post was still valid.

It seems all info is still valid with the exception of the -6 reading that only affected some minidsps.





Quote:
Again, I would stick to ~20-24db of headroom when testing with noise signal
http://www.meyersound.com/pdf/cinema...ech_report.pdf
This will be a great read. I've come across it in the last few days and have started, but not finished it. I've bookmarked it. Thanks for pointing it out!

Quote:
Important:I hope that you already have upgraded you miniDSP audio plug-in so that the input RMS meters are reading correctly.
Yes- I double checked. I have the latest version.




Quote:
From here on on your post, I read conflicting numbers and some high voltage readings. What is going on?
Quote:
With what instrument do you measure the signal amplitude?
I used a 60 hz sine wave to test initial output of the AVR pre-amp. Max out was 10.6 volts with max volume and sub trim.

I then set the AVR master listening level until my meter read 70% of max volts. That turned out to be +1.5 on the AVR master volume., or 7.42 volts on the meter.

From this point I used the AVR to calibrate my subs to a 75db reading, which brought the sub trim to -7.

I used a digital multi meter, it's nothing fancy.

From here I tested the mini-dsp input using the mini-dsp meters only, and my numbers above were incorrect (apologies I should have grabbed my notes). They are as follows-

AVR volume +1.5
Sub Trim -7 (75db calibrated)
This gave approximately -15 on the input meters while playing pink noise @ -3dbfs.

Everything the exact same- I then upped the sub trim to to +3 (10 db hot) and the mini-dsp input meter reads approximately -4.5.

Everything now the same again (AVR +1.5, sub 10 db hot) I listened to a mix of jazz/rock/rap. The input meter read -0.1 to -0.2 frequently.

I am happy to measure with just a sine wave. However....

I don't want to make this thread about how to fix my situation.

I wanted to make sure I was understanding some key points in your research. I share the same feelings as what others have already said over and over throughout this thread, including yourself.

Proper documentation should be put together for the potential and current owners of the mini-dsp.

Again- thank you for all the time you've spent on this.

Maybe I'll start another thread about my issues and if so I'd really like it if you chimed in.



Quote:
Which is your AVR model?
It's a Pioneer SC-1522k , should be the same as an sc68 without the elite badge.

Quote:
George
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Old 23rd December 2013, 09:08 PM   #45
vadi is offline vadi  Austria
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Thank you for measuring this. I am not sure how the 24dB boost-limit works with the crossover section, maybe you tested this (I am using the 4-way crossover plugin):
Let's say I apply 24dB boost in the preEQ at 10Hz, and this frequency is attenuated in the crossover section by at least -30dB for example, for all channels. Could 10Hz be boosted again in the individual channel section?
(because after preEQ the crossover lowers the level at 10Hz, and after that the individual boost is added again?)
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Old 24th December 2013, 11:47 AM   #46
gpapag is offline gpapag  Greece
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Yes Vadi, I have tested this.
Whatever you do with filters and crossovers of miniDSP, it is the sum of all the boosts/cuts that counts.

In your particular example at 10Hz:
(+24db)+(-30db)= -6db
You can boost the 10 Hz another 30db for to reach the limit of 24db boost.

If you exceed this limit by say 2db, then you have to attenuate 2db with the input attenuator but then this input attenuation will affect the whole frequency spectrum).

George
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Old 29th April 2014, 05:03 AM   #47
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Hello George-

I just read the Meyer's sound paper, again. And between that paper and your help here in this thread I think I know the answer but I have to ask for re-assurance.

Even though I'm using a sine wave generator to watch the meters, I still would be best with ~ 20 db of headroom due to the non-uniform 'reference' standard used by the different studios?
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Old 30th April 2014, 06:08 PM   #48
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Quote:
Originally Posted by gpapag View Post
Yes Vadi, I have tested this.
Whatever you do with filters and crossovers of miniDSP, it is the sum of all the boosts/cuts that counts.

In your particular example at 10Hz:
(+24db)+(-30db)= -6db
You can boost the 10 Hz another 30db for to reach the limit of 24db boost.

If you exceed this limit by say 2db, then you have to attenuate 2db with the input attenuator but then this input attenuation will affect the whole frequency spectrum).

George
I would think that it would be even worse - for instance, despite the overall -6dB level (+24)(-30)dB, the 24dB stage will internally exceed 0dB digital level before the output stage reaches 0dB, in fact 18dB before it.

I always try to minimize the boost in every stage, and apply any boost last. This often makes for a lot of reducing in gain between input and output so that the peak levels are not clipping.
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Old 13th August 2014, 05:23 PM   #49
adason is offline adason  United States
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I know this is an old thread, but I just have one quick question...I read the thread, but its slightly confusing. So when you apply steady sine wave 0.9Vrms to 2x4 minidsp, revA, that is full signal, what does the input and output signal level meter show? Assuming no eq, or attenuation is done in digital domain. Thanks.
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Old 14th August 2014, 01:25 AM   #50
Davey is offline Davey  United States
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Quote:
Originally Posted by adason View Post
I know this is an old thread, but I just have one quick question...I read the thread, but its slightly confusing. So when you apply steady sine wave 0.9Vrms to 2x4 minidsp, revA, that is full signal, what does the input and output signal level meter show? Assuming no eq, or attenuation is done in digital domain. Thanks.
The max input on these before clipping is closer to about 0.95VRMS. If you input that level the meters will show very close to "0.0".

Dave.
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