Need to figure out some SAC system basics

[KeithAbbott]

Our church is looking at a project to move the sound person from the sound booth - where its veeerry difficult to hear what's really going on - to the floor. At the same time we're looking at upgrading our present 20+ year old 16x4 BIAMP mixer.

At the moment, our auditorium is 120x120x18 (though it may be resized to 100x100 to add some additional rooms) and our style/music is conservative southern gospel and tradtional. Our output setup is currently simple: mono house speakers, a set of mono foldbacks, stereo recording, and a mono out that drives speakers in the nursery in a different wing.

I began researching our options, which I originally thought were going to be another analog board, or a digital board. Then I began running across information about SAC and realized there was a third option in the mix.

We're in the very early consideration stage but at the recommendation of a friend, we were looking at the Allen-Heath GL2400 24 or 32 channel for the analog option. The cost of that, a long 32x8 snake, and a quality roll top sound desk could put us nicely along the way toward a digital/virtual solution.

My experience level with professional digital audio is 0: my analog experience is, frankly, not much higher. I wish to spend the church's money wisely and wind up with a solution that will carry us well into the future. SAC certainly looks like an option with the flexibility to do that.

However, in order to know where I stand, I have to understand all of the pieces so I can determine costs. If the cost gets too far beyond the cost of an analog console and expense of moving it into the auditorium, the board wont approve it.

I***8217;ve read through the FAQ and forum and didn***8217;t really find a cohesive, comprehensive description of all of the equipment needed, and the considerations in the selection of that equipment. Actually I didn***8217;t even find a basics of ***8216;here***8217;s the pieces, how they fit together, and what they do***8217;. (maybe another sticky?) Although the faq gives pretty good hints.

Based on what I***8217;ve read here, I***8217;ve made some guesses that I***8217;d to air them out before everyone and have you help me correct and round them out. And since I***8217;m a visual type person, Ive done a drawing (sorry) that I***8217;ll include.
Please correct and add anything that needs it.

In the drawing, I***8217;ve shown everything (that I know about so far) that is required to replace an analog console with a SAC system, in the light gray box.

The centerpiece ***8211;the one this forum is about ***8211; is of course, the SAC software which runs on a Windows-based PC ***8211; requirements covered in faq I believe, but fast single CPU is better than slower dual.

SAC provides the mixing console and signal processing ***8211; compression, n-gate, channel assignment, and a thousand (well 993) other things. Some features require additional plugins ***8211; some free, some chargeable. I***8217;m not sure what is what with the plugins ***8211; perhaps someone can list some examples to help clarify. The software and PC are shown roughly in the middle of the drawing.

There has to be some way to get the inbound signals from mics etc, and the outbound signals to amps etc, into the PC to be processed. This is the job of the audio interface card (internal PCI card as recommended by moderator ***8211; there seem to be external device offerings supporting firewire as well). For the purposes of the drawing, I specifed the RME 9652s since it was one suggested by the moderator. (A side note here that I read specs on the 9632 also and am starting to suspect I've mentally mixed up the specs of the 2).
This type of card supports 3 ADAT interfaces, which are optical interfaces ***8211; each of which can support 8 channels of audio in or out. There are other interface formats available (MADI for instance) but I don***8217;t know what the pros and cons are for using 1 over the other or if they will work with SAC (assumably so), or what alternate hardware would have to be used with them.
The card specs say that it can support 16 channels in or out (with expansion cards). I am not sure if 8 in and 8 out is possible on one card and I am not sure why there are 3 ADATs on the board since 16 channels could be supported by 2 ADATs. Also when I looked at the expansion cards, I didn***8217;t see any that were specified for the 9652 so I***8217;m not sure how you get to 16. I assume without the expansion card you get 8?
For the cards, there are specs for bit depth and sampling rate and I know the basics on those specs and the associated controversies related to bit depth. Without jumping into the argument, it sounds like its better to use 24-bit for mixing and recording (does that include even basic House of Worship live service recording where exacting results are not expected like they are in production recording?)
The Audio Interface cards are shown in the drawing as inserted into the PC. Since I don***8217;t know the story of what is required to get 16 channels per card on these, I***8217;ve shown 4 cards to get a 24x8 console. Hopefully someone can set me straight here.
One of the options for the board is a world clock. It appears that the clock provides special syncing of the audio signals. I am not sure if these are recommended, required, or only needed in special cases. If they are required or recommended, is it 1 per card, 1 per console, or some other measurement.

Finally, the Audio Interface Cards support digital channels ***8211; not analog, so there has to be an analog to digital converter for incoming signals from all those mics and junk, and a digital to analog converter for outgoing signals to all those foldback and house amps.
Again, the drawing shows one of the FAQ recommended devices, the behringer ADA8000. Each unit provides 8 ports of IO. Inputs have their own preamps. I***8217;m not sure what kind of overhead is available in the preamps, and if these inputs will universally connect to anything (phantom powered mic, non-powered mic, line level from playback devices and wireless receivers, laptops, etc) and I***8217;m not sure if each channel is independently assignable as an input or an output. I presumed so and in the drawing they are shown at the left edge of the ***8216;mixer box***8217; (the gray area) with some miscellaneous inputs and outputs connected.
The ADA8000s connect to the PCI Audio Interface cards via the ADAT interfaces. In the drawing, the bottom ADA8000 shows 2 ADAT cables connected 1 for input and 1 for output. This may be wrong.
Undoubtedly there are other devices supporting this function but I don***8217;t know what the recommendations are (other than if you***8217;re using an interface card with a MADI interface, your AD converters better support a MADI interface.

So that***8217;s it. The mic signal comes in to an ADA, where it hits a preamp ***8211; (I don***8217;t know how gain/atten is controlled in the preamp ***8211; if it is settable, fixed, or automatic).
It***8217;s then converted to digital and sent along the ADAT pipe to the PCI Audio interface card, which provides multiple channels for this type input.
The PC then provides mixing and signal processing ***8211; although it seems that some of this must be offloaded to the audio card since these cards are supposed to keep CPU impact to a minimum.
The PC then sends the processed signal out the audio interface card to a D/A unit ***8211; in this case still the ADA8000 ***8211; where it***8217;s converted back to analog and sent to the amp. I don***8217;t know if it***8217;s still recommended to have a limiter between the amp and ADA8000 as final protection for the amp and speakers or not.
There it is. I know it has to be full of holes and errors. Please help me correct my understanding and fill it out so I can move on to the next step of deciding what equipment we would need/use in our implementation.

(Sorry about the image - I really had to size it down to make it acceptable)

Thanks
K