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Author Topic: gain staging a digital rig, DSP, and powered speakers  (Read 24407 times)

Mac Kerr

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #20 on: September 28, 2013, 05:11:05 pm »

For the record, the range is +24 dBU (01V96) to +16 dBU (ADA8000), an 8dB range.

Fine, whatever. The point is that there is zero benefit in having the speaker protection begin at 0dBfs. You never want to get near that level in the console. In the days of analog, having the meter buried in the red meant it was more than 3dB above +4dBm, and some harmonic distortion would start at some level above that. That was probably a reasonable level to have protection kick in. Having protection begin at +16dBm when that is the absolute digital maximum before all hell breaks loose is not a reasonable level.

While turning the speakers down till they don't hit the limiters till 0dBfs will keep them from ever hitting the red limiter that has danger zone written on it, driving the console to 0dBfs to get enough gas out of the speakers will probably cook the drivers the first time it happens. The high frequency content of a clipped digital signal is a thing of wonder. In the end, there is no way, none, to protect speakers from a user determined to overdrive them. To quote Ian Malcolm from Jurassic Park, "life will find a way".

Mac
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Scott Wagner

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #21 on: September 28, 2013, 05:24:34 pm »

Given your stated goals, I would set the system where 0dBFS is where the hard limit (red) lights come on.  That would cause you to run out of everything at the same point.  Of course, that could cause some engineers to run the mix hotter than they should.  If they want the most out of the system, they'll be running beyond -12dBFS.  I really don't like to go there.

I use -12dBFS as my maximum, and set amplifier sensitivity to give the desired output for the space de jour.
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Scott Wagner
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Bob Leonard

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #22 on: September 28, 2013, 05:45:11 pm »

Bob,

I can't actually follow your thought here. Are you talking about a specific level? The term 0dB without any reference doesn't mean anything. Mark's original point was referring to 0dBfs, the maximum digital level of his console. In his case with multiple output devices that equated to output levels ranging from +16dBu to +20dBu, varying device to device. His plan to adjust the output levels of the higher output devices down to match the lowest is a good one because every output will be the same at the same console level. Without that adjustment there would be as much as a 4dB difference between outputs for the same signal routed to them.

Mac

Mac,
0dBfs at the console followed by no increase or decrease in level or volume at any point or device. I.E. If an EQ were placed in line after the console output there would be no additional gain, loss of gain, increase or decrease in volume.
 
@ Mark - In the case of your cabinets, and after reading the manual, RCF states for normal operation the setting for the "sensitivity control" should be set to the detent, which is +4db. What is not known is this. does the control react as more of a volume control, or sensitivity control.
 
Regardless, I would place the control in the recommended position (+4db) and lower the final output level at the DSP. In that manner the system should be now set for unity gain and the only setting change required will be at the DSP. Once set those system settings should result in safe operating levels without the use of a limiter. In the picture below this is done with a 4800 using the "master gain" setting of the DSP. The picture does not represent my system or any specific system.
 
 
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Mac Kerr

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Re: digital vs analog level
« Reply #23 on: September 28, 2013, 05:56:34 pm »


Mac,
0dBfs at the console followed by no increase or decrease in level or volume at any point or device. I.E. If an EQ were placed in line after the console output there would be no additional gain, loss of gain, increase or decrease in volume.

Bob, 0dBfs is not in and of itself an audio level. It only refers to the internal digital level at which the console runs out of ones and zeros. In Mark's case that could be an audio level of +16dBm, +20dBm, or +24dBm. The analog level of the analog side of a digital console are determined by the characteristics of the particular AD or DA convertor.

Mac
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Mark McFarlane

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #24 on: September 28, 2013, 11:53:09 pm »

If at 0 dbFS console, speaker soft clip happens, then you will never even hit that soft clip. That is sacrificing some headroom that can be used under reasonable circumstances. You should be able to tickle those soft limiters, but you can't tickle 0dbFS. You know what I mean? Wouldn't you want to set it all up so that red (damage) would be 0dbFS, so that you never hit red (because you never hit 0dbFS)?

Although I can trust myself to not run at 0 DBFS, I'm not sure other operators can be so trusted.

Still, I get your point, I'd be wasting some headroom, the solution seems to be to get it 'right below' the red limiter at 0 DBFS, or change the speaker setting when I am not operating, but that's not entirely practical since the only time I am not operating is when I'm onstage with a band or two at festivals, i.e. I'm operating 6 hours and onstage 2 hours,....
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Mark McFarlane
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Mark McFarlane

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #25 on: September 28, 2013, 11:57:30 pm »

Fine, whatever. The point is that there is zero benefit in having the speaker protection begin at 0dBfs. You never want to get near that level in the console. In the days of analog, having the meter buried in the red meant it was more than 3dB above +4dBm, and some harmonic distortion would start at some level above that. That was probably a reasonable level to have protection kick in. Having protection begin at +16dBm when that is the absolute digital maximum before all hell breaks loose is not a reasonable level.

While turning the speakers down till they don't hit the limiters till 0dBfs will keep them from ever hitting the red limiter that has danger zone written on it, driving the console to 0dBfs to get enough gas out of the speakers will probably cook the drivers the first time it happens. The high frequency content of a clipped digital signal is a thing of wonder. In the end, there is no way, none, to protect speakers from a user determined to overdrive them. To quote Ian Malcolm from Jurassic Park, "life will find a way".

Mac

Thanks Mac, I understand what you are saying. 

To overcome my fear of someone else overdriving the speakers by putting the console at 0 DBFS, I guess I can put some tape over the master fader slot at -12 or some such,...
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Mark McFarlane
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Turn down what's too loud.

Mac Kerr

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #26 on: September 28, 2013, 11:59:23 pm »

Although I can trust myself to not run at 0 DBFS, I'm not sure other operators can be so trusted.

They certainly can't be trusted to not run at 0dBfs when that is the only way to get full output from the system.

Mac
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Mac Kerr

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #27 on: September 29, 2013, 12:04:55 am »

Thanks Mac, I understand what you are saying. 

To overcome my fear of someone else overdriving the speakers by putting the console at 0 DBFS, I guess I can put some tape over the master fader slot at -12 or some such,...

Taping down a fader does not limit the console level, they'll just drive some other part of the console into clipping. Seriously, make a plan that gets the operating levels of the system down to something reasonable. Limit the output of the console if it makes you feel better, but if you let people use it who feel they have to run it into the red to get loud enough they are going to do it, and eventually they are going to break things. Needing to run a system at its limits is a sign of not enough system.

Mac
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Bob Leonard

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Re: digital vs analog level
« Reply #28 on: September 29, 2013, 12:09:27 am »

Bob, 0dBfs is not in and of itself an audio level. It only refers to the internal digital level at which the console runs out of ones and zeros. In Mark's case that could be an audio level of +16dBm, +20dBm, or +24dBm. The analog level of the analog side of a digital console are determined by the characteristics of the particular AD or DA convertor.

Mac

Thanks Mac. I stand clarified. I think we're both saying the same thing, however, it seems my language requires some translation. Probably because half of my brain is still stuck in an analog world.
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Tim Padrick

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #29 on: September 29, 2013, 04:12:01 am »

If the amps are clipping, most folks won't notice if it's not too much too often.  If something else in the chain is clipping too, it sounds like crap in a hurry.  I like to have at least 10dB of headroom in everything ahead of the amps (unless the amps have 20dB more power than I'll ever use).

The Alesis can definitely be a 'choking point'.
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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #29 on: September 29, 2013, 04:12:01 am »


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