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Author Topic: Mic level straight through a DSP  (Read 2701 times)

Jeff Breen

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Mic level straight through a DSP
« on: March 07, 2012, 03:12:06 pm »

I'm pretty sure I know this answer without having to try it...and I hate for my first question here to be kind of dumb but here it goes...

I'm considering using an open architecture DSP in a sound system in order to provide an automatic mix mode and alternate signal routing for a manual mix mode...in other words, take analog signal in and either process and mix them automatically and output them to the power amps, or take those analog inputs and send them 1 to 1 out the analog outputs for mixing on an analog board...then take the boards mix outputs and bring them back into the DSP for speaker processing prior to feeding the amps.

This is straight forward and common stuff and I've done it before.  In the past I've limited the mic's that can have their signal routed to the analog mixer to what I know I can control, like wireless receivers, since these are permanently installed I can apply the gain at the analog input stage of the DSP and feed the analog mixer a line level signal.  In this project I'd like to take XLR inputs from stage pockets into the analog inputs of the DSP and pass them right through to the outputs with no gain.

Why?  I was thinking I would take advantage of the DSP's digital analog bus to make a cheap digital snake.  The end user would just have plug a patch cable into the wall and trigger the "manual mix mode" preset.  Shortly after I thought of this I realized I'd be sending mic level signal through an ADC with no gain prior, bury the signal in the processor's noise floor, through a DAC stage and then amplified by the input stage of a cheap analog mixer.

So, my question.  Is there any possible way I can do this and somehow get acceptable signal quality?  What specs might I look at if I wanted to try and determine this?  Could I take the dynamic range, subtract it from the max signal level before clipping to determine if the system noise floor is low enough (impossibly low, I imagine) to allow a mic level signal to pass through at a high enough relative level to be unaffected? 

And what else might I consider to provide a simple to use system allowing automix mode and manual mode, that the uninitiated and very tentative volunteer can set up and operate? 
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Brad Weber

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Re: Mic level straight through a DSP
« Reply #1 on: March 07, 2012, 03:22:33 pm »

Why?  I was thinking I would take advantage of the DSP's digital analog bus to make a cheap digital snake.
That may be where the concept differs from what you envision as the preamps are part of a digital snake and what you get out is line level.  So mic level into the DSP and line level out is emulating a digital snake.

You might be able to take the mics into the console and then use the insert to go into the DSP and back out of it as line level, however that means the mixing console preamps are always part of the signal chain.

I personally typically approach it differently, using analog splits to split the mic inputs on the DSP and into mixer inputs, then using the DSP to switch between a preset routing an internal automixer to the DSP outputs and a preset that routes the mixing console outputs to the DSP outputs.
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Mac Kerr

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Re: Mic level straight through a DSP
« Reply #2 on: March 07, 2012, 04:16:14 pm »

I'm considering using an open architecture DSP in a sound system in order to provide an automatic mix mode and alternate signal routing for a manual mix mode...in other words, take analog signal in and either process and mix them automatically and output them to the power amps, or take those analog inputs and send them 1 to 1 out the analog outputs for mixing on an analog board...then take the boards mix outputs and bring them back into the DSP for speaker processing prior to feeding the amps.

This is straight forward and common stuff and I've done it before.  In the past I've limited the mic's that can have their signal routed to the analog mixer to what I know I can control, like wireless receivers, since these are permanently installed I can apply the gain at the analog input stage of the DSP and feed the analog mixer a line level signal.  In this project I'd like to take XLR inputs from stage pockets into the analog inputs of the DSP and pass them right through to the outputs with no gain.

Why?  I was thinking I would take advantage of the DSP's digital analog bus to make a cheap digital snake.  The end user would just have plug a patch cable into the wall and trigger the "manual mix mode" preset.  Shortly after I thought of this I realized I'd be sending mic level signal through an ADC with no gain prior, bury the signal in the processor's noise floor, through a DAC stage and then amplified by the input stage of a cheap analog mixer.

So, my question.  Is there any possible way I can do this and somehow get acceptable signal quality?  What specs might I look at if I wanted to try and determine this?  Could I take the dynamic range, subtract it from the max signal level before clipping to determine if the system noise floor is low enough (impossibly low, I imagine) to allow a mic level signal to pass through at a high enough relative level to be unaffected? 

And what else might I consider to provide a simple to use system allowing automix mode and manual mode, that the uninitiated and very tentative volunteer can set up and operate?

I only know of one digital audio system that does not use mic pres before the AD conversion, and I assume you are not talking about a Stagetec Nexus. In the system you describe there are mic pres in the DSP before the AD conversion which will still be in the circuit if you route the digital signal somehow to the mixing console.

I can think of 3 alternative methods, two of which involve a router. The most straightforward would be to split all the mic signals to both the DSP and the console and have a way to changeover the inputs of the DSP from the mic line to the console outputs. This could be a router, or manual changeover box like the Radial SW8.

The other way would be to use a router or changeover switch to switch everything, mic lines between console and DSP, and DSP inputs between mic lines and console outputs.

A third method would be to have a mic level patchbay where everything is normalled to the DSP, but can be patched however you want it when you need to use the console. This is basically what we do for a corporate event I do every month in the company's auditorium.

Mac
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Hayden J. Nebus

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Re: Mic level straight through a DSP
« Reply #3 on: March 12, 2012, 07:33:22 pm »

I only know of one digital audio system that does not use mic pres before the AD conversion, and I assume you are not talking about a Stagetec Nexus. In the system you describe there are mic pres in the DSP before the AD conversion which will still be in the circuit if you route the digital signal somehow to the mixing console.

I can think of 3 alternative methods, two of which involve a router. The most straightforward would be to split all the mic signals to both the DSP and the console and have a way to changeover the inputs of the DSP from the mic line to the console outputs. This could be a router, or manual changeover box like the Radial SW8.

The other way would be to use a router or changeover switch to switch everything, mic lines between console and DSP, and DSP inputs between mic lines and console outputs.

A third method would be to have a mic level patchbay where everything is normalled to the DSP, but can be patched however you want it when you need to use the console. This is basically what we do for a corporate event I do every month in the company's auditorium.

Mac

I have two venues that utilize symetrix symnet processing. Each has an 8x8 with L,C,R,sum mix inputs and 4 dedicated automix inputs. The units are fed via a pach bay with the automix inputs normalled
open, so as to encourage sequencer use when patching condenser mics, avoiding !kapow! effect.
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ProSoundWeb Community

Re: Mic level straight through a DSP
« Reply #3 on: March 12, 2012, 07:33:22 pm »


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