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post #31 of 69 Old 06-18-2019, 04:21 AM
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Originally Posted by johnson636 View Post
Currently, all speakers are set to small. So your statement holds true for the 2x4 HD as well? Are you saying neither the regular 2x4 nor the HD is the correct piece of equipment for bass duty? In regards to input clipping avoidance.
The 2x4HD can take 4Vrms on the input, which is better, and can output 2Vrms. So it's probably just adequate for many people. The balanced 2x4 can take 4Vrms input and can output 4Vrms (only using a balanced output).

You also need to keep in mind that many people are trying to boost the signal in their MiniDSP at some frequency or frequencies (house curve & EQ'ing), so that means they need to dial back the overall gain on the MiniDSP in order to gain headroom for the frequencies they are boosting. notnyt touches on the other point of whether you can get the full rated power from your amp with the signal or not. When combining these two factors you could fairly readily be in a situation where there isn't a combination of gain and level trim settings where you can avoid clipping the input or output signals from the MiniDSP, be able to drive your amp to it's full rated power, while simultaneously setting the subwoofer to the right level for 85dB playback with a -30dBFS signal.

An example:

The 2x4 Balanced and 2x4HD will clip their input at about the same point as most Denon receivers clip their output. They will actually just barely clip a 0dBFS signal in the LFE channel played at reference with the subwoofer trim at 0dB (all processing bypassed). To allow for redirected bass (if you listen at reference) without clipping the Denon should probably have the level trim set to about -6dB. This is then safe for the input of the MiniDSP 2x4HD (4V setting) or the 2x4 Balanced. However, if you're applying any filters in the MiniDSP that add gain at any frequencies you need to reduce the overall gain in the MiniDSP by a corresponding amount. So if you have some filters for EQ or a house curve that give you say 8dB of gain somewhere in the frequency range of 5-120Hz you need to pull down the gain in the miniDSP on the input by 8dB to prevent internal clipping. This now means you've reduced your LFE chain by 14dB from what's coming out of the receiver (which itself is dialed back from 0dB). 6dB from the 4V input to 2V output loss just going through the miniDSP, and 8dB from the internal MiniDSP gain adjustment. The overall efficiency of the subwoofer system and gain of the amp have to overcome all these gain reductions.

The output of the MiniDSP is what it is. Sure, you can say, "Well, I can get 2Vrms (balanced 2x4HD) out and that's more than my amp needs to make full rated power into the load." but that doesn't consider if you can still calibrate the sub to 85dB with a -30dBFS .1 signal. My opinion is that the latter is more important than making full power. If you can set the "gain" knob on your amp to any setting and achieve the correct SPL output level after you've set everything to make sure you don't get clipping in the signal chain in front of the amp I say you're done. IMHO, whether you can still make your full rated power from your amp is largely irrelevant. Maybe you'll clip the output of the amp from a lack of amp power or maybe your amp will never make more than half it's rated power, but the amp will be getting a clean signal on the input and your sub will playing back at the right SPL up to reference (assuming the amp isn't under powered and clipping the output) and that's the best scenario.
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post #32 of 69 Old 06-18-2019, 06:30 AM
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Originally Posted by Stereodude View Post
The 2x4HD can take 4Vrms on the input, which is better, and can output 2Vrms. So it's probably just adequate for many people. The balanced 2x4 can take 4Vrms input and can output 4Vrms (only using a balanced output).

You also need to keep in mind that many people are trying to boost the signal in their MiniDSP at some frequency or frequencies (house curve & EQ'ing), so that means they need to dial back the overall gain on the MiniDSP in order to gain headroom for the frequencies they are boosting. notnyt touches on the other point of whether you can get the full rated power from your amp with the signal or not. When combining these two factors you could fairly readily be in a situation where there isn't a combination of gain and level trim settings where you can avoid clipping the input or output signals from the MiniDSP, be able to drive your amp to it's full rated power, while simultaneously setting the subwoofer to the right level for 85dB playback with a -30dBFS signal.

An example:

The 2x4 Balanced and 2x4HD will clip their input at about the same point as most Denon receivers clip their output. They will actually just barely clip a 0dBFS signal in the LFE channel played at reference with the subwoofer trim at 0dB (all processing bypassed). To allow for redirected bass (if you listen at reference) without clipping the Denon should probably have the level trim set to about -6dB. This is then safe for the input of the MiniDSP 2x4HD (4V setting) or the 2x4 Balanced. However, if you're applying any filters in the MiniDSP that add gain at any frequencies you need to reduce the overall gain in the MiniDSP by a corresponding amount. So if you have some filters for EQ or a house curve that give you say 8dB of gain somewhere in the frequency range of 5-120Hz you need to pull down the gain in the miniDSP on the input by 8dB to prevent internal clipping. This now means you've reduced your LFE chain by 14dB from what's coming out of the receiver (which itself is dialed back from 0dB). 6dB from the 4V input to 2V output loss just going through the miniDSP, and 8dB from the internal MiniDSP gain adjustment. The overall efficiency of the subwoofer system and gain of the amp have to overcome all these gain reductions.

The output of the MiniDSP is what it is. Sure, you can say, "Well, I can get 2Vrms (balanced 2x4HD) out and that's more than my amp needs to make full rated power into the load." but that doesn't consider if you can still calibrate the sub to 85dB with a -30dBFS .1 signal. My opinion is that the latter is more important than making full power. If you can set the "gain" knob on your amp to any setting and achieve the correct SPL output level after you've set everything to make sure you don't get clipping in the signal chain in front of the amp I say you're done. IMHO, whether you can still make your full rated power from your amp is largely irrelevant. Maybe you'll clip the output of the amp from a lack of amp power or maybe your amp will never make more than half it's rated power, but the amp will be getting a clean signal on the input and your sub will playing back at the right SPL up to reference (assuming the amp isn't under powered and clipping the output) and that's the best scenario.
Very informative response. So even if I'm able to boost the output signal of the mini (ROLLS MB15b Promatch and More) the issue still remains of clipping the 2v input of the mini. It sounds like you're not a fan of the minidsp, before I go out and purchase a balanced 2x4, what device would you recommend?

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post #33 of 69 Old 06-18-2019, 06:44 AM
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Originally Posted by johnson636 View Post
Very informative response. So even if I'm able to boost the output signal of the mini (ROLLS MB15b Promatch and More) the issue still remains of clipping the 2v input of the mini. It sounds like you're not a fan of the minidsp, before I go out and purchase a balanced 2x4, what device would you recommend?
I'm not a big fan. I think it's only just barely adequate if you're careful, but there's no other choice on the market if you want to manipulate frequencies below 20Hz. That said, I have a 2x4 balanced unit and have used it for years. I recently got a 2x4HD and intend to see how it does replacing the 2x4 balanced unit. I'm pretty sure I have enough gain left to have the 2Vrms output not be an issue vs. the 4Vrms I get from the 2x4 balanced. I suggested to the miniDSP folks years ago that they make a miniDSP specifically for subwoofers with higher voltages, like 8Vrms I/O and a lower sampling rate, but it went nowhere. They couldn't see the need for those sorts of voltage levels despite the simple fact that they're readily present in the LFE signal chain.

If you don't need to go below 20Hz IMHO the QSC DSP-30 is a better product.
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post #34 of 69 Old 06-18-2019, 06:59 AM
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Originally Posted by Stereodude View Post
I'm not a big fan. I think it's only just barely adequate if you're careful, but there's no other choice on the market if you want to manipulate frequencies below 20Hz. That said, I have a 2x4 balanced unit and have used it for years. I recently got a 2x4HD and intend to see how it does replacing the 2x4 balanced unit. I'm pretty sure I have enough gain left to have the 2Vrms output not be an issue vs. the 4Vrms I get from the 2x4 balanced. I suggested to the miniDSP folks years ago that they make a miniDSP specifically for subwoofers with higher voltages, like 8Vrms I/O and a lower sampling rate, but it went nowhere. They couldn't see the need for those sorts of voltage levels despite the simple fact that they're readily present in the LFE signal chain.

If you don't need to go below 20Hz IMHO the QSC DSP-30 is a better product.
Well it looks like a balanced mini is a must because I must boost below 20Hz in my room. With the balanced 2x4 in the chain, is there any benefit of having the ROLLS MB15b Promatch in the chain?

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post #35 of 69 Old 06-18-2019, 07:05 AM
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I have some amps that are just straight amps but I'd like to have a gain knob on them, not just an attenuation knob. The amps only have an RCA (unbalanced) input. I used an ART CleanBox and it really can add gain but my AVR has unbalanced and the Cleanbox can only output balanced when the input is unbalanced.

Basically, I would like the CleanBox gain but in an unbalanced to unbalanced configuration.
Not sure if something like this would work: https://www.performanceaudio.com/rol...ine-mixer.html
I like how on my plate amps they have a gain knob. Thoughts on how to add gain knob like functionality to a consumer amp?

http://rolls.com/product/DA134

The rolls 134 will give you lots of gain and 4 outputs to boot for quite cheap. No infrasonic bass loss either. Probably work well for those with
the usual output gain problems even with a mini dsp. Here the unit would install after the dsp.

If you have a balanced mini dsp, I would suggest putting a matchbox ahead of it. As Wayne will tell you, there are plenty of matchboxs with
excellent specifications.

Personally I have a hard time seeing the 2 volt input as an issue. If it was, would it not be an issue already, if your supposed avr measured 9 volts or even 4 volts. My experience is that all rca outputs are for the most part inadequate in driving an XLR output. (throwing all the measuring out the window, to date I see no warnings for people to measure the rca outputs just to hook up other rca equipment, all rca equipement is suppose to be compatible)

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post #36 of 69 Old 06-18-2019, 07:16 AM
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Well it looks like a balanced mini is a must because I must boost below 20Hz in my room. With the balanced 2x4 in the chain, is there any benefit of having the ROLLS MB15b Promatch in the chain?
There's no way for me to answer that. It depends if you can set everything up to avoid clipping up to your intended maximum playback level and are still able to set the subwoofer to achieve the proper SPL at your seat from a given test tone. If you can, then there's no benefit. If you can't you need something to increase the signal level. It's not entirely clear how much voltage the Promatch can output. If they mean +18dBu when they say +18dB max output (balanced) it should do ~6.15Vrms. That's not much of a boost from the 4Vrms the balanced 2x4 miniDSP can do, only about +3dB.
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post #37 of 69 Old 06-18-2019, 08:20 AM
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There's no way for me to answer that. It depends if you can set everything up to avoid clipping up to your intended maximum playback level and are still able to set the subwoofer to achieve the proper SPL at your seat from a given test tone. If you can, then there's no benefit. If you can't you need something to increase the signal level. It's not entirely clear how much voltage the Promatch can output. If they mean +18dBu when they say +18dB max output (balanced) it should do ~6.15Vrms. That's not much of a boost from the 4Vrms the balanced 2x4 miniDSP can do, only about +3dB.
But if the Promatch is installed after, lets say an 2x4 HD, and the HD has 4Vrms output but needs 6Vrms total in order to get the desired spl at the MLP, wouldn't the Promatch's 6.15Vrms be available to subsidize the 2x4 HD? Another question, if I were to apply a LS filter of 8db, would I have to adjust the gain 8db or would I have to factor in each frequency that receives the 8db boost?

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post #38 of 69 Old 06-18-2019, 08:33 AM
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But if the Promatch is installed after, lets say an 2x4 HD, and the HD has 4Vrms output but needs 6Vrms total in order to get the desired spl at the MLP, wouldn't the Promatch's 6.15Vrms be available to subsidize the 2x4 HD?
Yes, it could get you ~3dB of gain.

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Another question, if I were to apply a LS filter of 8db, would I have to adjust the gain 8db or would I have to factor in each frequency that receives the 8db boost?
Presumably you're talking about a +8dB shelf to some frequency range. You would need to lower the gain at the input side of MiniDSP in the software GUI by 8dB to prevent clipping at frequencies where you have that 8dB of gain being applied. If you have more frequencies being boosted to EQ you sub you'll need to take that into account also.
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post #39 of 69 Old 06-18-2019, 08:49 AM
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Yes, it could get you ~3dB of gain.


Presumably you're talking about a +8dB shelf to some frequency range. You would need to lower the gain at the input side of MiniDSP in the software GUI by 8dB to prevent clipping at frequencies where you have that 8dB of gain being applied. If you have more frequencies being boosted to EQ you sub you'll need to take that into account also.
If you don't mind me asking, why are you attempting to replace the 2x4 balanced with the 2x4 HD? Curiosity perhaps?

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post #40 of 69 Old 06-18-2019, 10:31 AM
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If you don't mind me asking, why are you attempting to replace the 2x4 balanced with the 2x4 HD? Curiosity perhaps?
I'm hoping my system will have less hum with it. Long story really short I have some sort of ground loop like issue from my HTPC and other equipment that only shows up in my sub when the balanced miniDSP is in the system or I don't lift the ground pin on my HTPC. If the receiver is connected directly the sub there's no issue even with the HTPC is properly grounded. I'm hoping the 2x4HD will not have the same issue.

I also wanted to try out the BassEQ stuff and it often uses more than the 6 filters the non HD 2x4 models can do.
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post #41 of 69 Old 06-18-2019, 12:06 PM
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The 2x4 Balanced and 2x4HD will clip their input at about the same point as most Denon receivers clip their output. They will actually just barely clip a 0dBFS signal in the LFE channel played at reference with the subwoofer trim at 0dB (all processing bypassed).
wat?

denon 5308.. I haven't seen any denon's clip their output with a full scale signal with all trims set to 0, but I also haven't poked at any of the bottom end ones.

fs input over hdmi, +12db mv, +10.5db subs
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post #42 of 69 Old 06-18-2019, 05:11 PM
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wat?

denon 5308.. I haven't seen any denon's clip their output with a full scale signal with all trims set to 0, but I also haven't poked at any of the bottom end ones.

fs input over hdmi, +12db mv, +10.5db subs
And by bottom end you mean top of the line. The 4520CI definitely does.



A -0.01dBFS 40Hz DTS encoded .1 signal from the subwoofer output at 0dB (Reference) on the master volume without clipping. Before making any measurements I turned off Audyssey, set all the speaker & sub trims to 0dB, and set all the speakers to the same distance.
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And by bottom end you mean top of the line. The 4520CI definitely does.



A -0.01dBFS 40Hz DTS encoded .1 signal from the subwoofer output at 0dB (Reference) on the master volume without clipping. Before making any measurements I turned off Audyssey, set all the speaker & sub trims to 0dB, and set all the speakers to the same distance.
Wow, that's poor. Are the other channels as bad?
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Originally Posted by johnson636 View Post
If you don't mind me asking, why are you attempting to replace the 2x4 balanced with the 2x4 HD? Curiosity perhaps?
I'm hoping my system will have less hum with it. Long story really short I have some sort of ground loop like issue from my HTPC and other equipment that only shows up in my sub when the balanced miniDSP is in the system or I don't lift the ground pin on my HTPC. If the receiver is connected directly the sub there's no issue even with the HTPC is properly grounded. I'm hoping the 2x4HD will not have the same issue.

I also wanted to try out the BassEQ stuff and it often uses more than the 6 filters the non HD 2x4 models can do.
The ART Cleanbox will give the gain option and remove the groundloop issue

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post #45 of 69 Old 06-18-2019, 07:34 PM
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Wow, that's poor. Are the other channels as bad?
As you'd expect, they're 10dB less, so no they don't clip with a 0dBFS signal at reference.

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The ART Cleanbox will give the gain option and remove the groundloop issue
I'm not so sure about that. The best I can tell it's not actually a ground loop issue. It sounds like one, but I'm pretty sure it's a hum put onto the balanced signal lines by the MiniDSP.
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post #46 of 69 Old 06-20-2019, 04:45 PM
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Ok, here is what I did to ensure my minidsp 2x4 wasn't clipping it's input and outputs. In order to check the levels of the output on the mini and check the output voltage on the amps, I took a neutrik cable with one end with bare wire, then took my DMM/oscilloscope and took measurements

1.Set AVR MV at 0db
2.Mute the outputs in Minidsp or disconnect subs from the amp
3.Use REW to send a 50Hz sine wave at -3dBFS
4.Attenuate the input in the Mindsp software until there is no clipping
5.Be sure to attenuate the signal to leave headroom or PEQ gain adjustments

FP20k amp output voltage
15Hz - 40Hz Roughly 122v

I wonder if I were to get a balanced 2x4, I coud get to 140v on the outputs without clipping
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How was your PC running REW connected to your AVR and how did you determine there was or wasn't clipping in step #4 ?
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post #48 of 69 Old 06-20-2019, 04:52 PM
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Originally Posted by Stereodude View Post
How was your PC running REW connected to your AVR and how did you determine there was or wasn't clipping in step #4 ?
REW was connected via hdmi and I used the input and out meters with the minidsp software. It should be visible in the photos.

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post #49 of 69 Old 06-20-2019, 08:38 PM
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Originally Posted by johnson636 View Post
REW was connected via hdmi and I used the input and out meters with the minidsp software. It should be visible in the photos.
The meters show signal level, I'm not following how they can show clipping.
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post #50 of 69 Old 06-21-2019, 06:44 AM
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Originally Posted by Stereodude View Post
The meters show signal level, I'm not following how they can show clipping.
My bad. I thought they were clipping meters I can connect my scope on the outputs, but do you have a way to measure the inputs?

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post #51 of 69 Old 06-21-2019, 07:33 AM
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Originally Posted by Stereodude View Post
And by bottom end you mean top of the line. The 4520CI definitely does.



A -0.01dBFS 40Hz DTS encoded .1 signal from the subwoofer output at 0dB (Reference) on the master volume without clipping. Before making any measurements I turned off Audyssey, set all the speaker & sub trims to 0dB, and set all the speakers to the same distance.
Many AVR's don't have enough headroom to add WCS redirected bass to WCS LFE and will clip the waveform very early. There was some discussion and testing of units at DB years back. The Oppo players failed badly from what I remember.

I wonder how many people running extremely boosted BassEQ settings through minidsp's are listening to a distorted clipped mess?
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post #52 of 69 Old 06-21-2019, 07:39 AM
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Originally Posted by Ricci View Post
Many AVR's don't have enough headroom to add WCS redirected bass to WCS LFE and will clip the waveform very early. There was some discussion and testing of units at DB years back. The Oppo players failed badly from what I remember.

I wonder how many people running extremely boosted BassEQ settings through minidsp's are listening to a distorted clipped mess?
Did the discussion yield a method of compensating for the redirected bass?

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post #53 of 69 Old 06-21-2019, 10:11 AM
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Originally Posted by Ricci View Post
I wonder how many people running extremely boosted BassEQ settings through minidsp's are listening to a distorted clipped mess?
BassEQ should be safe because it doesn't result in clipping the way Aron is doing them. Running an aggressive house curve or additional EQ could on top of it could result in clipping. But that clipping can and will happen without the BassEQ too, just maybe not as often. I'd guess many people with a MiniDSP who listen near reference have clipping in the LFE chain and don't realize it. Especially the people who are running their subs 10+dB hot unless all that boost is done with their amp's "gain" knob.

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Originally Posted by johnson636 View Post
Did the discussion yield a method of compensating for the redirected bass?
They don't clip internally (generally). So you just have to turn the LFE channel trim(s) down. Keep the subwoofer trim in your reciever no higher than -6dB and you should probably be okay.

FWIW, the Sherbourn pre-pro I have clips internally and there's no work around.
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post #54 of 69 Old 06-21-2019, 11:53 AM
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Originally Posted by Stereodude View Post
BassEQ should be safe because it doesn't result in clipping the way Aron is doing them. Running an aggressive house curve or additional EQ could on top of it could result in clipping. But that clipping can and will happen without the BassEQ too, just maybe not as often. I'd guess many people with a MiniDSP who listen near reference have clipping in the LFE chain and don't realize it. Especially the people who are running their subs 10+dB hot unless all that boost is done with their amp's "gain" knob.


They don't clip internally (generally). So you just have to turn the LFE channel trim(s) down. Keep the subwoofer trim in your reciever no higher than -6dB and you should probably be okay.

FWIW, the Sherbourn pre-pro I have clips internally and there's no work around.
Do you have a method of testing the inputs without the gear you and Notnyt are using?

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post #55 of 69 Old 06-21-2019, 11:59 AM
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Originally Posted by johnson636 View Post
Do you have a method of testing the inputs without the gear you and Notnyt are using?
You can do it with a true RMS multimeter. You can probably do it with the MiniDSP's meters too, but you have to follow a particular process.

A simple check is to play your -3dBFS RMS test tone (in the LFE channel over HDMI) from REW with the master volume of your receiver at -10dB with the subwoofer trim at 0dB. If you measure more than -10dB on the meters in the miniDSP GUI you're going to get clipping on the input of the miniDSP when you turn up to 0dB.
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post #56 of 69 Old 06-21-2019, 12:12 PM
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I performed that process that is reflected in the attachments in post# 46. I sent a 50Hz -3dBFS (REW) via hdmi, to the lfe channel. The MV was set to 0 and the input and outputs were set so they read -10 on the signal meters. Oh, the -10 reading was with all my filters in place.

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post #57 of 69 Old 06-21-2019, 12:35 PM
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Originally Posted by johnson636 View Post
I performed that process that is reflected in the attachments in post# 46. I sent a 50Hz -3dBFS (REW) via hdmi, to the lfe channel. The MV was set to 0 and the input and outputs were set so they read -10 on the signal meters. Oh, the -10 reading was with all my filters in place.
You need to do the test with the input "gain" adjustments on the MiniDSP all the way up, which it seems you didn't do.
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post #58 of 69 Old 06-21-2019, 01:04 PM
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You need to do the test with the input "gain" adjustments on the MiniDSP all the way up, which it seems you didn't do.
I started the test with input gains all the way. I adjusted the gains down until I was able to read -10 signal level after each filter. Is that not the proper method?

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post #59 of 69 Old 06-21-2019, 01:35 PM
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Originally Posted by johnson636 View Post
I started the test with input gains all the way. I adjusted the gains down until I was able to read -10 signal level after each filter. Is that not the proper method?
No, because it if starts out reading 0dB when receiver is at 0dB and the subwoofer trim is at 0dB it could be clipping. You have to bring the MV and/or the subwoofer trim down on the receiver down until the MiniDSP doesn't read 0dB (with the gain in the MiniDSP up all the way). Then you know you're not clipping the input of the MiniDSP. I'd suggest you want the input level on the MiniDSP no higher than -6dB with the -3dBFS RMS test tone from REW (with the MiniDSP gain all the way up) at whatever the loudest volume you'll play back from your receiver is. Then you'll have some headroom for redirected bass and won't be able to clip the input of the MiniDSP at the loudest volume you intend to play back at.
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post #60 of 69 Old 06-21-2019, 02:45 PM
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Originally Posted by Stereodude View Post
No, because it if starts out reading 0dB when receiver is at 0dB and the subwoofer trim is at 0dB it could be clipping. You have to bring the MV and/or the subwoofer trim down on the receiver down until the MiniDSP doesn't read 0dB (with the gain in the MiniDSP up all the way). Then you know you're not clipping the input of the MiniDSP. I'd suggest you want the input level on the MiniDSP no higher than -6dB with the -3dBFS RMS test tone from REW (with the MiniDSP gain all the way up) at whatever the loudest volume you'll play back from your receiver is. Then you'll have some headroom for redirected bass and won't be able to clip the input of the MiniDSP at the loudest volume you intend to play back at.
But isn't each method essentially the same since the objective is getting the signal level at or below than -6 on the minidsp? My sub trim is set at -6 and the MV of the avr is at 0 because that's easy to remember.
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