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  #1  
Old 06-14-2016, 09:11 PM
MarkH MarkH is offline
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Default Unbalanced Outboard Gear to HD I/O 16x16

I have a question about running my Unbalanced outboard gear (analog synths, drum machines) to the HD I/O 16x16 analog DB25 inputs.

I will use Unbalanced cables connected from the gear. As some may already have experienced, using Balanced cables on Unbalanced outputs causes a gain reduction. The only thing I plan to put between the Unbalanced gear/cables and the HD 16x16 is a 48 point patch bay.

Most 1/4" 48-point patch bays are TRS (Balanced). I'm guessing since the cables connecting to the patch bay from the outboard gear is unbalanced, it is not an issue to have a TRS patch bay? For the cables connecting from the patch bay to the HD I/O, I cannot find a DB25 snake that is Unbalanced 1/4" to DB25. It seems like I would need to use a DB25-TRS snake from the HD I/O to the patch bay. I'm trying to figure out if there will be gain issues.

Any suggestions are appreciated.
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Old 06-14-2016, 09:24 PM
Darryl Ramm Darryl Ramm is online now
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

Why do you want to run unbalanced cables or want an unbalanced patch panel? Just wire up your rack/studio with everything balanced and just plug yer unbalanced stuff in.

Just test what works for the final cable to the instrument, most stuff should work fine with balanced cables, but if not use a unbalanced cable into the synth etc. (it depends on the quality/exact TS/TRS socket they use, how old it is, and how it's really wired).

Since the interface balanced input is seeing a single sided signal, you are may see a -6dB decrease in signal level (not strictly "gain"). Wha exactly happens can be more complex and I'm not sure what the circuit looks like in the HD analog ins. But there is nothing you can do to avoid that with wires/how you connect things, but why does it really matter? make it up during mixing.

The thing to worry about is noise. If that's a problem look at isolating grounds etc. or a transformers input and/or using a preamp with DI etc. or buy better equipment with balanced IO, or even better that connect digitally.

Last edited by Darryl Ramm; 06-14-2016 at 09:43 PM.
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  #3  
Old 06-15-2016, 05:48 AM
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arche3 arche3 is offline
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

It's not an issue of balanced vs. Unbalanced. The issue is you need the drum machines and synth modules to be connected to a mixing board line inputs or the lineup inputs on some mic pres to bring the output levels up to go into your avid interface. The avid interface is just the input into the system. You need the proper gain staging before the input. Maybe some drum machines and synth modules can have a hot enough output to bypass a gain stage of a mixing board or mic pre but I think not in most cases. Your question is Akin to asking if you can connect a microphone directly into the avid interface. You cannot if you are following standard recording methods.

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Old 06-15-2016, 08:18 AM
MarkH MarkH is offline
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

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Originally Posted by arche3 View Post
You need the proper gain staging before the input.
Gain Staging is probably the best way to summarize it. I did some playing around last night. I'll provide a couple of examples.

If I connect the Unbalanced output from my drum machine (Yocto 808) directly to a patch bay or to a DB25 Snake connected to the input of the HD I/O, the input gain can be very low even when the drum machine is turned all the way up. If I use an Unbalanced cable and run the same Unbalanced output from the drum machine to the Omni HD INST input, the volume level is where I would expect it to be and I start adjusting the volume on the drum machine.

Another example. I've got a Studio Electronics Code 8 synth. It has 16 outputs (8 stereo) which are Unbalanced. I'm using the individual outputs instead of the combined stereo output because I have the Discreet Op Amps on the individual outputs. The 16 outputs are connected to an Alesis MultiMix 1U Line Mixer. The Alesis line mixer inputs are unbalanced, but then stereo main output is balanced. I'm guessing due to proper gain staging, this is why if the Alesis connects to the HD I/O the input levels are fine (and volume can be adjusted on the Alesis). If I try running the 16 individual outs from the Code 8 (or the combined stereo out of the Code 8) directly to the HD I/O, the input gain is once again too low.

Short of buying a mixer to gain stage, I noticed there are 8 channel, 1U Direct Input boxes available, making it easy to connect unbalanced gear and sending a balanced signal (I think) out of the DI box. The DI has the option of engaging a 20+ db boost per channel.

Perhaps the DI solution is an acceptable solution. It is cost-effective over buying a mixer, which I really don't want to have to deal with anyway.
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  #5  
Old 06-15-2016, 09:28 AM
Darryl Ramm Darryl Ramm is online now
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

Stop fixating on balanced vs. unbalanced that is unlikely your issue. And the more you talk about it the more you are going to drive yourself into confused/wrong decisions or get wrong advice here.

Likely like your gear is not outputting +4dBu line level anything, balanced or not. If the output level or impedance your gear has needs a DI or preamp then use one. What gain did you use on the DI on the Omni? If you have an omni then why not use it's DI? Don't just go buying any old DI box until you understand what Gain you were using and what gain that DI offers. And you don't need to nail inputs to within a few dB, the HD IO 24 bit converters have enormous dynamic range/great S/N. You just want to be somewhat in the ball park and focused on good S/N from the analog synth outputs (and preamp/DI chain if you are using that)..

Last edited by Darryl Ramm; 06-15-2016 at 09:44 AM.
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  #6  
Old 06-15-2016, 01:07 PM
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arche3 arche3 is offline
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

Get a 8 channel rack mount mic pre with light pipe. Or get 2 for 16 channels. Lots of models out there. Problem solved.

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Old 06-18-2016, 04:53 PM
MarkH MarkH is offline
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

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Originally Posted by arche3 View Post
Get a 8 channel rack mount mic pre with light pipe. Or get 2 for 16 channels. Lots of models out there. Problem solved.

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Thanks for the input, everyone. It really comes down to 3 options.

1) Use Mic Pre (my friend uses Universal Audio 4-710d for his vintage synths)
2) Use a DI unit to convert/boost the unbalanced signal to balanced
3) Input everything directly to the -10dB inputs in HD I/O and adjust the gain input on each channel. I haven't tried this yet but I'm guess the HD I/O has enough headroom to boost the signal

I've learned a lot as not all Unbalanced outputs are the same on various synths and drum machines. My legacy Oberheim OB-8 has a weak output (all OB-X, OB-Xa, and OB-8 units do) compared to others, like my Alesis Andromeda or WMD/SSF Monolith.
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Old 06-18-2016, 05:16 PM
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albee1952 albee1952 is offline
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

1) Use Mic Pre (my friend uses Universal Audio 4-710d for his vintage synths) Yes, do this as it solves all your problems.

2) Use a DI unit to convert/boost the unbalanced signal to balanced
A DI does not exactly do this. It converts a high-impedance unbalanced instrument source(which you have) to a balanced mic-level source(which you still need a preamp for)

3) Input everything directly to the -10dB inputs in HD I/O and adjust the gain input on each channel. I haven't tried this yet but I'm guess the HD I/O has enough headroom to boost the signal
Read the manual that came with your HD IO as it says very clearly that unbalanced connections MUST NOT ground the cold side(which is exactly what happens when you plug a standard TS cable(as you would use with most drum machines and keyboards) into a balanced TRS patchbay. I would use a preamp, but the 4-710D might be pricey for this purpose.

Having said all that, you could save lots of cash and use something like SMPro's EP84. http://www.smproaudio.com/index.php/...s/preamps/ep84

One last option; if you are good at soldering, you could make "quasi-balanced cables to connect your unbalanced keyboards to balanced inputs(the -10 inputs on the HD IO), but these need to be wired correctly. Using balanced cable(assuming white and black wires, plus shield), connect the unbalanced end as tip=white, sleeve=black(do not connect the shield at this end). At the balanced end, the TRS plug would be tip=white, ring=black, sleeve=shield.
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  #9  
Old 06-18-2016, 05:23 PM
Darryl Ramm Darryl Ramm is online now
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

Quote:
Originally Posted by albee1952 View Post

2) Use a DI unit to convert/boost the unbalanced signal to balanced
A DI does not exactly do this. It converts a high-impedance unbalanced instrument source(which you have) to a balanced mic-level source(which you still need a preamp for)
Talking about DIs get confusing as it's not clear wether people are talking about external DI boxes or mic preamps with DIs in. A mic preamp with DI in allows a lot of gain variation, an active DI with gain trim allow some depending on model.
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Old 06-18-2016, 08:16 PM
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paulo m paulo m is offline
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Default Re: Unbalanced Outboard Gear to HD I/O 16x16

Quote:
Originally Posted by albee1952 View Post
1) Use Mic Pre (my friend uses Universal Audio 4-710d for his vintage synths) Yes, do this as it solves all your problems.

2) Use a DI unit to convert/boost the unbalanced signal to balanced
A DI does not exactly do this. It converts a high-impedance unbalanced instrument source(which you have) to a balanced mic-level source(which you still need a preamp for)

3) Input everything directly to the -10dB inputs in HD I/O and adjust the gain input on each channel. I haven't tried this yet but I'm guess the HD I/O has enough headroom to boost the signal
Read the manual that came with your HD IO as it says very clearly that unbalanced connections MUST NOT ground the cold side(which is exactly what happens when you plug a standard TS cable(as you would use with most drum machines and keyboards) into a balanced TRS patchbay. I would use a preamp, but the 4-710D might be pricey for this purpose.

Having said all that, you could save lots of cash and use something like SMPro's EP84. http://www.smproaudio.com/index.php/...s/preamps/ep84

One last option; if you are good at soldering, you could make "quasi-balanced cables to connect your unbalanced keyboards to balanced inputs(the -10 inputs on the HD IO), but these need to be wired correctly. Using balanced cable(assuming white and black wires, plus shield), connect the unbalanced end as tip=white, sleeve=black(do not connect the shield at this end). At the balanced end, the TRS plug would be tip=white, ring=black, sleeve=shield.
If you want to skip the need to use a mic preamp/DI combination to interface the unbalanced line outs of the gear, the use of a unbalanced to balanced converter will keep everything at line level, this way the TRS patch can be used at ease. There´s various models on the market for stereo or multichannel, here´s an example of a device I did use a lot in the past for the same purpose as the OP:

http://www.canford.co.uk/SONIFEX-RED...TERFACES-Input

It´s also worth noting that the use of a TRS patchbay for mic signals is not advisable as each time you insert the jack you momentarily short circuit the sleeve and cold. Preamps don´t like that, in particular when phantom power is on.

Regarding the use of the-10 dbv inputs on the HD I/O, yes, you need at least 6 db of gain to compensate. I used this inputs several times for connecting semi pro gear and used a plugin like EQ1(with no eq applied) that has gain adjustment, on the channels fed by those inputs. It can be any plugin that has gain, but the idea is to spare the cpu load, so I opted for this.

One of the disavantages of using the -10dbv inputs on the HD I/O at the same time of the normal +4dbu inputs is that you need to make sure the correct channels are selected on the I/O hardware menu for each of the 8 channels available as either +4dbu or -10dbv. In a fixed instalation is OK, other than that you need to keep changing it.
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