Compatibility questions
T.O. Ross
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#1
19th February 2013
Old 19th February 2013
  #1
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Thread Starter
Compatibility questions

First post here. I have been lurking and reading for a couple of weeks -- didn't really see these specifics addressed.

I am looking at putting a rig together for location recording, with the equipment rack and computer close to either the monitor desk or the FOH console. Performance is primary and cost is a distant second. Potential for expansion is also a consideration.

Attached is a shot of the gear that will be in the equipment rack as well as a shot of the Holophone H2-PRO surround sound microphone. The Holophone will be used as an audience / ambience mic and can also take the system into the world of multi-channel surround sound recordings.

The three blue devices at the top are combination mic splitters / mic preamps from XTA Electronics in the UK – model DS8000.

Below those are two Sytek MPX-4Aii four-channel mic preamps, made in USA.

The analog-to-digital converters are at the bottom – they are made-in-USA Benchmark ADC16s.

The specs for the ADC16 say maximum input level at maximum gain = +6 dBu @ 0 dBFS. This should work well with the outputs from the Sytek mic preamps. I am wondering about the XTA DS8000's output levels:

Code:
Nominal signal level, relative to 0dB gain  Electronic 0dB     Transformer -10dB 
Maximum output level into 600R              Electronic +20dBu  Transformer +10dBu
Ideally I would like to use the transformer outputs from XTA to Benchmark but I'm not sure the transformer outputs will have enough steam to drive the ADC16 properly. Will they?

Next question -- from the Benchmark website:

Two 6-conductor FireWire 400 connectors allow daisy chaining with other FireWire devices.

This tells me that the computer we use will only need to have a single FireWire port. I am thinking that either a Mac Mini or a MacBook Pro loaded with options should be a good choice. Each of these is equipped with one FireWire 800 port. We'll use an external Thunderbolt drive for audio recording and playback. Has anyone tried chaining two ADC16s together?

I am also thinking that Pro Tools 10 (not HD / HDX) is an OK way to go. From the Avid Pro Tools 10 website:

• 96/48/24 maximum simultaneous audio tracks @ 48/96/192 kHz

• 32 maximum simultaneous audio recording tracks

Pro Tools 10 will give us the ability to record up to 32 tracks at once (up to 24 from the stage mics and DIs plus up to eight from the Holophone surround mic) at 96kHz. Should work in theory -- does anyone have practical experience to share?

Thank you to any and all who respond and thanks for this great site!

Ross
Attached Thumbnails
Compatibility questions-isp-rack-mic.jpg  
#2
19th February 2013
Old 19th February 2013
  #2
Lives for gear
I suggest familiarizing yourself with operating levels and how they work.

The Benchmark ADC16 for instance has +8 dBu to +28 dBu input sensitivity range (at 0 dBFS) which can be configured per input (the manual says something slightly different so you'd have to get them to fix their typo).

Since the output of your XTA transformer is +10 dBu, naturally do the math and you can trim the ADC16 input sensitivity to work with that piece so that it easily clips the ADC16. This is how that works: if the ADC16 is trimmed to produce 0 dBFS with +8 dBu in, then of course +10 dBu from the XTA will also clip the ADC16, by 2 dB. You'll want to keep the default trim on the inputs from the Sytek because that is +24 dBu.

Benchmark describes the operation of the Firewire interface on their website, but I would contact them to see if it will work as you want--daisy chaining two ADC16's.

I see no reason to doubt Avid's statements about how many channels Pro Tools native can record and play back.
T.O. Ross
Thread Starter
#3
19th February 2013
Old 19th February 2013
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Quote:
Originally Posted by brew View Post
I suggest familiarizing yourself with operating levels and how they work.

The Benchmark ADC16 for instance has +8 dBu to +28 dBu input sensitivity range (at 0 dBFS) which can be configured per input (the manual says something slightly different so you'd have to get them to fix their typo).

Since the output of your XTA transformer is +10 dBu...
Thank you for the reply.

+10 is the maximum output level rating for the XTA's transformer outputs. Their nominal output level is rated to be -10 dB. Hence my question. It seems to me that it would take a signal that is much hotter than the signal from a mic to coax +10 out of one of the XTA's transformer outputs. If my math is right, a nominal -10 signal from the XTA would yield a signal level of -18 dBFS on the Benchmark side.

Thanks again for your reply.

Cheers,

Ross
#4
19th February 2013
Old 19th February 2013
  #4
Lives for gear
I suggest that your math reveals a misunderstanding about levels. Max IO level is the only relevant number--nominal level is irrelevant.
  1. The ADC16 ships set to 0 dBFS = +24 dBu. This is quite easy then to understand that +10 dBu would equal -14 dBFS.
  2. You can alter the ADC16 input level setting to be anything between 0 dBFS = +8 dBu through +29 dBu.
  3. If you connect the XTA transformer out (+10 dBu) to the ADC16 input and do nothing to the ADC16 trim levels, in your DAW you will never peak past -14 dBFS. Why is this so? Because 24-10=14.
Quote:
If my math is right, a nominal -10 signal from the XTA would yield a signal level of -18 dBFS on the Benchmark side.
Your math is not right. The XTA clearly has 20 dB of headroom (max level - nominal level = 20). Using the math from above, 14-20 = -34 dBFS. That's where your nominal signal level would be in the digital domain if you did not alter the cal of the ADC16.

"Nominal" is not a universally agreed upon level, which is why you can ignore it. A manufacturer could choose a different nominal level for their gear, and this is a fine example. The ADC16 ships with a nominal level of +4 dBu, with 20 dB headroom (the well accepted SMPTE standard). The XTA transformer out also has 20 dB headroom, but the nominal is -10 dBu! Clearly nominal in this case is not the same.

Also, your note about mic level is not quite right--the XTA is a preamp, and all the outputs are post preamp. It is not a traditional passive mic splitter, so it would likely be easy to achieve +10 dBu at the output with a microphone.

I hope the attached graph makes it clear.
Attached Thumbnails
Compatibility questions-levels.png  
T.O. Ross
Thread Starter
#5
19th February 2013
Old 19th February 2013
  #5
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Thread Starter
Thank you for the graph -- and for your patience. Makes a lot more sense now!

Cheers,

Ross
#6
19th February 2013
Old 19th February 2013
  #6
Lives for gear
 

reaper for both the stability and lack of ilok. You can drop the files in PT easily for mix later, or j.
T.O. Ross
Thread Starter
#7
20th February 2013
Old 20th February 2013
  #7
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Quote:
Originally Posted by nnajar View Post
For a location rig, I would suggest reaper for both the stability and lack of ilok. You can drop the files in PT easily for mix later, or just mix in reaper.
Noted -- thank you for the reply. I will look into how Reaper files can be dropped into Pro Tools.

Thanks again,

Ross
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