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Author Topic: gain staging a digital rig, DSP, and powered speakers  (Read 24406 times)

Bob Leonard

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #10 on: September 27, 2013, 07:41:41 pm »

Mark,
Do you have access to a signal generator?
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Mac Kerr

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #11 on: September 27, 2013, 09:34:35 pm »

Note, I never said I would be running the console at 0 DBFS, I just proposed that 0 DBFS on the console would be the point where the speakers just started going into their first stage of limiting.

If the speaker limiters start their first stage limiting at 0dBfs where does the second stage start?

Your idea of setting all your analog outs to be the same makes sense, your idea of having anything but total disaster happen at 0dBfs not so much. With an analog output of +16dBu at 0dBfs, and allowing for 12dB of headroom, your maximum intended analog out should be +4dBu (the old 0Vu standard) which will be -12dBfs. If you start your limiters 6dB above that you will have plenty of headroom in the audio chain prior to the analog outputs, and also plenty of drive level to keep any gear working at fairly high signal levels.

The maximum output of the console should not be considered a protection device for your speakers. It is much more likely to be the end of them.

Mac

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Bob Leonard

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #12 on: September 28, 2013, 01:27:55 am »

Mac,
I'm hoping my statement above doesn't read as using the board output is my recommendation for the OP. My statements meant to read that the final device signal out, and the signal out for all devices previous, (without a limiter) should be 0db. 0db being no increase or decrease in signal level at any point.

In the case where 0db is more signal than can be safely handled by the final device, the speakers, then the signal will obviously need to be lowered, so that when 0db is reached at the board output and up through the last device damage to the speaker does not occur and at least 6db headroom is available in reserve.

In what may seem to be contrary to popular belief I have always set my signal chain to unity up and through to the last device prior to the amplifiers. That has always been a DSP or crossover, or in the rare case where neither of those are required, the system EQ. With that method I then set the DSP, crossover, EQ output to the final output level. Doing this is actually much easier today then ever before. Any good DSP or crossover will allow changes to input and output level on a per channel basis.

Today, and at least in my digital world, the final output from the desk is much more easily set for any and every output to any and every device including FOH, monitors, IEM, etc., mitigating the need to set the final level of output at the system DSP, in my case a 4800.

I do not see this as limiting as this does not fit the definition of limiting. I see this as setting the final output to a proper and usable level, a level that when set at 0db on the board can supply no more than maximum usable power to the speakers without incurring damage.

My question concerning the signal generator was about to point to a simplistic method for setting the gain structure of the OP's rig. Pump a signal into a channel, set the channel and board gain to 0db, then follow the signal through each successive device until the gain structure is set for 0db up to the DSP and then adjust accordingly. Just a poor mans method for setting system gain IMO. But I could be wrong.
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Mark McFarlane

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #13 on: September 28, 2013, 02:24:44 am »

Mark,
Do you have access to a signal generator?

I have the one in Smaart 7 (and one built into the console)
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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 #14 on: September 28, 2013, 03:43:47 am »

Let me try a different way of asking the final question...

A quick recap on the rig:

01V96>DEQ830>ADA8000>DSP    for L, R, Sub, + 1 more channel (usually a monitor channel with no processing)
01V96>DEQ830>ADA8000            for 4 additional channels (usually my monitors go here)

The DSP has limiters, but they are not currently engaged, I only use the DSP for crossover, delay, and some sub EQ (i.e. system alignment). The powered speakers have built in limiters, as described in the original post.

a) I now have all my devices registering 0 DBFS at the same signal level
The DEQ830 and 01V96, connected by ADAT, were already in sync as expected, but to sync the DSP, connected analog to the ADA8000 I adjusted the analog input gain on the DSP

b) I now have all my devices outputting a maximum of +16 dBu
This requires setting output attenuation on the DSP (-4) and 01V96 (-8) to match the max ADA8000 output level (actually, I haven't done this step yet... but plan to).

There is a sensitivity knob on the back of each of my powered speakers. 

Question: What is the step-by-step procedure you would follow to set the speaker's built-in-amp sensitivty knob to (a) prevent inadvertent damage to the speakers, particularly when I am not the operator, (b) get maximum (safe) SPL from the system, (c) preserve maximum S/N.
« Last Edit: September 28, 2013, 04:49:29 am by Mark McFarlane »
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Mark McFarlane
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Bob Leonard

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #15 on: September 28, 2013, 08:19:26 am »

Just what I described above Mark. The sensitivity knob will not limit the amount of produced power output from the amplifier. It is NOT a volume knob. Your choice is a limiter, a device I refuse to use, or setting the final output to a level which can not push the amplifier(s) to a point where damage will occur. My choice has always been the latter.

D. Turn the sensitivity knob all the way up and if amplifier hiss occurs, turn the sensitivity down until it is no longer heard, then forget those knobs exist.
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Mac Kerr

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #16 on: September 28, 2013, 01:00:05 pm »

Mac,
I'm hoping my statement above doesn't read as using the board output is my recommendation for the OP. My statements meant to read that the final device signal out, and the signal out for all devices previous, (without a limiter) should be 0db. 0db being no increase or decrease in signal level at any point.

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
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Mark McFarlane

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #17 on: September 28, 2013, 04:06:29 pm »

Your choice is a limiter, a device I refuse to use, or setting the final output to a level which can not push the amplifier(s) to a point where damage will occur. My choice has always been the latter.

This is exactly what I originally proposed, to set the built-in amp/dsp sensitivity so that the built-in amp/dsp goes into first stage limiting just before the console gets to 0 DBFS.

So my initial proposal was correct?

...

D. Turn the sensitivity knob all the way up and if amplifier hiss occurs, turn the sensitivity down until it is no longer heard, then forget those knobs exist.

This sentence ('turn it all the way up') seems in conflict with your previous sentence (turn it to the limit point).

If I follow this procedure (sensitivity all the way up) on my TT22A's (there is very little hiss), and with the 01V96 outputs at 24 dBu, then the TT22A built-in amps will start their second stage limiting (in the red) when the console gets around -25 DBFS and I'll lose half my fader throw. Anything continuous above -25 DBFS will blow my speakers.

In contrast, if I set the TT22a sensitivity at around 2/10, I can go up to 0 DBFS on the console and just be tickling the TT22A built-in amp/dsp first stage limiter (and perhaps lose, as some have suggested, 3-6db of SPL between first and second stage limiters)

It seems kind of silly to set the amp level so high (even if it isn't hissing) that I can only use the bottom half of the consoles master fader.

Sidebar: The TT22A speaker sensitivity knob may not be classified as a 'volume control', but the SPL output by the speakers changes from extremely soft to ear damaging loud as I turn this knob clockwise, so it does control the 'volume'.

There must be some conceptual gap in my understanding, or in the language we are using.
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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 #18 on: September 28, 2013, 04:13:31 pm »

.... In his case with multiple output devices that equated to output levels ranging from +16dBu to +20dBu, varying device to device. ...

For the record, the range is +24 dBU (01V96) to +16 dBU (ADA8000), an 8dB range.
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Mark McFarlane
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Turn down what's too loud.

Samuel Rees

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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #19 on: September 28, 2013, 04:27:36 pm »


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

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)?
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Re: gain staging a digital rig, DSP, and powered speakers
« Reply #19 on: September 28, 2013, 04:27:36 pm »


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