snake replacements

[wydsiwyrg]

I have recently been reading of a system to route 64 channels of ADAT I/o along a single Cat5 cable, obviously this would be a much nicer system than trad. snakes - but my question is - since most 8 channel A/Ds have gain control on them - what are the big implications of having the channel gains at the stage, rather than at the mixer? (Of course you'd have a trim tho)..

Also - what is the difference between using TRS against XLR inputs.. such as all the decent D/As I've found have had TRS outputs (cept the Berry, has XLR outputs)... what are the implications of doing this?

Have any of you been using alternatives to trad. snakes?

Tim

[Solstace]

Ello...

 

Some background:

 

My regular fixed system uses an Allen and Heath IDR8, which I believe can (sorta) be used in the way you're intending. We're only really using it to provide system management, such as "per-user" desk recalls (useful when different engineers use different grouping, etc) alongside FOH EQ and speaker management. It also allows us to patch our radio-mics in, so that someone can use a separate dedicated control surface to operate the system if only speech is requires. Perhaps this is overkill, but given that not many of our guys and dolls are competent or even trained engineers, we decided this was the most "idiot-proof" way of doing things - imagine asking a complete newbie to mix speech using up to 8 channels on our 48-ch ML4000!! We'd never get PLI, that's for sure!!!

 

We did consider running a larger version of the IDR system so that we could use 2 runs of Cat5 (and appropriate hardware) in place of fitting a large multicore. In the end we decided to go with traditional multicore, with the following reasoning:

 

1) cost of primary installation - we figured that our new system (installed in Nov/Dec 2003) would last 20 years or more. In that time for the same money, we can either replace the "lo-tech" multicore 5 times (though it's unlikely we'll need to do so more than once or twice in that time) or we can buy the "hi-tech" solution. This brings me conveniently to:

 

2) the fact that the new digital media hasn't been around long enough for common time/use failures to become apparent, and we didn't want to be the first to notice problems, nor to bear costs that we cannot reasonably predict.

 

3) the stage boxes for squirting audio up&down the cat5 cable do indeed have the preamps (and dac's/buffers, where appropriate) in them. I have two issues with this. First off, to control things like gain, phantom switching etc, we would need to leave a PC or laptop permanently connected to the unit to control it, giving little or no protection over core system settings. Secondly, the pre-amps in such a unit are unlikely to compare favourably with those found in many higher-end desks.

 

4) our engineers are digital luddites - most of them can't stand CD's, love vinyl and prefer to keep as much of the signal path as possible in the analogue domain. While I love the hiss-free clarity of (uncompressed) digital recordings/systems, with live sound I do have to agree that analogue is the way forward for now. Perhaps the changeover phase (no pun intended) is happening around about now.

 

5) Friends of mine have had too many bad experiences of loud digital hash being sent to amps/speakers when a digital desk or processor (such as an Ultracurve) crashes. The last incidence cost £350 to replace the offending piece of kit, and over £3,500 to replace the amps and speakers it took with it on its way out!!! Add to that a few hundred deafened punters who were in the auditorium at the time, it's not a pretty picture!

 

As for using TRS (I'm guessing by this you mean balanced jacks) instead of XLR at the desk channel input, there's not going to be too much difference in the long run. The sound through the desk will essentially be the same, though all things being equal I would think that the TRS inputs ought to have a slightly lower noise floor than the XLR inputs, given that XLR inputs are most commonly catering for mic-level signals while TRS Jack inputs tend to deal with line-level signals (and let's not get started about -10dB or +4dB line levels!

 

Hope some (or all) of this helps.

 

C.

[david.elsbury]

Also - what is the difference between using TRS against XLR inputs.. such as all the decent D/As I've found have had TRS outputs (cept the Berry, has XLR outputs)... what are the implications of doing this?

<{POST_SNAPBACK}>

Generally TRS refers to a balanced signal, exactly like an XLR, except on a 1/4" jack. TRS jacks tend to be at line level though, because microphones use XLR connectors pretty much as standard. You need to be sure to use a balanced TRS-TRS cable to connect gear though, because if you plug a TS (Tip/Sleeve, Mono) jack in then it will unbalance the signal and I believe lower the signal level due to it becoming a -10dBu signal from a +4dBu signal. If you are making adaptor cables, XLR pin 1 to sleeve, XLR pin 2 to tip, and XLR pin 3 to ring.

 

Regards

David

[wydsiwyrg]

Generally TRS refers to a balanced signal, exactly like an XLR, except on a 1/4" jack. TRS jacks tend to be at line level though, because microphones use XLR connectors pretty much as standard. You need to be sure to use a balanced TRS-TRS cable to connect gear though, because if you plug a TS (Tip/Sleeve, Mono) jack in then it will unbalance the signal and I believe lower the signal level due to it becoming a -10dBu signal from a +4dBu signal. If you are making adaptor cables, XLR pin 1 to sleeve, XLR pin 2 to tip, and XLR pin 3 to ring.

 

Regards

David

<{POST_SNAPBACK}>

 

Thanks - sorry.. am a total beginner with sound and finding my way! Really appreciate your comments!

Tim

[Bobbsy]

I've used the Audiorail system a couple of times with relative success, but there are still issues.

 

First...as you've already identified by asking the question, moving the gain trims and phantom power switching away from the console does cause operational issues and some loss of functionality. Clearly, you can work around it but still it's not ideal.

 

Second, as Solstace identifies, it can be counterproductive in terms of quality of the mic preamps. One show I know of (that shall remain un-named) had the preamps in Behringer ADA8000s feeding, via Audiorail, into Midas pre amps at the other end.

 

Shurely shome mishtake her, occifer!

 

Lastly, another consideration not mentioned so far, can be latency. The best systems keep this down to (by memory...don't quote me) under 10 ms, but it can be a consideration.

 

Yes, there are places where all these trade offs can be worthwhile (one place I did use this sort of technology was a touring show where wheeling a preset rack to the stage and linking a single CAT5 back to the mixer saved a LOT of weight and set up time) but in most cases I'd still stick to a conventional snake. Indeed, putting my money where my mouth is, I bought a new analogue snake a couple of months ago!

 

Bob