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Re: arsclist Ground Impedance for Sound Studio

Title: Re: arsclist Ground Impedance for Sound Studio
Hello José,

I'm sorry I didn't get a chance to reply to your inquiries sooner.

Recently I have been involved in a number of installations for mixing theatres and DAWs in a post-production facility. In the transition from analog to digital, we had to answer many of the same questions you asked about grounding. While I am unable to discuss specific impedences, I will share some practical information on what we did. Please forgive me if I am too detailed or over-stating the obvious.

The first consideration is the quality of electricity going to your audio equipment. Where possible, all audio equipment should be on separate electrical circuits from all lighting, ventilation, and other non-audio loads (including film projectors, mag dubbers, and regular building services).

Also, if you are experiencing significant fluctuations in the electrical supply, you should seriously consider back-up power systems or a UPS (uninterupptible power supply), especially if you have upgraded to expensive and sensitive digital mixing and editing equipment.

In our studio's case, we had upgraded all audio-related electrical circuits to have isolated ground wires direct from receptacle to panel/ from panel to building ground. These isolated ground wires are not mechanically bonded to the electrical boxes or panels.

The building "ground" most often used in urban areas is a building's main water pipe which is guaranteed to travel tens of feet underground (that's our standard here, where it must go deep enough to withstand permafrost.)

All analog and digital audio equipment in the mixing and mastering theatres (excluding DAWs) should have an additional chassis ground - a grounding path completly separate from electrical and electronic wiring. Again, in our cases, all mixing consoles, recorders and audio processing equipment were rack-mounted, with each having a ground strap attached somewhere to the equipment chassis, then run to a copper grounding bar mounted in the rear of the rack.

The path was as follows*
*all grounding wire was stranded or solid copper, with an identifiable (green) jacket

1. Equipment chassis to each rack's grounding bar = #12 AWG ground wire
2. Rack's grounding bar to star ground (no more than 70ft distance) = #6AWG  ground
3. Star ground to building ground (may be several hundred ft) =#1 AWG ground wire

In many instances, the above grounding of equipment chassis is not necessary. However, when you are dealing with unreliable power sources, and highly sensitive digital equipment, these can prevent future problems. Also, if a ground hum does occur, you can try disconnecting the chassis of a given set of equipment as a process of elimination.

In addition to the chassis ground, the audio ground for analog XLR balanaced lines can also be a factor in ground loops. In some cases, doing a ground lift (leaving pin one unattached) at the destination end of an audio path is sufficient to maintain adequate signal quality, RFI rejection, while preventing the ground loop.

Depending upon the physical configuration & location of your networking and Digital Audio equipment, the same process may or may not apply. Chassis grounds are similarly applicable to rack-mounted equipment. However when it comes to the link between DAW host computers and the audio interface boxes, there is extra potential for ground hum.

Some DAW hardware has a duplication of power source - where the computer powers the sound card bus, and the Interface box is powered, but power is being sent through the audio cable from sound card to interface. Add to the chain a small powered mixer, and the audio grounding becomes further looped. Its important to establish a ground lift in the appropriate audio connectors, to solve this hum.

Stand-alone DAW's generally do not require extra grounding. However, once they enter a network configuration, the issues I've just outlined will become more relevant. For the computer-network side of things, isolated ground power receptacles should be adequate. Although computer networks are not my area of expertise, my experience with the duplicate power DAW mentioned above tells me that erring on the side of ground isolation, as opposed to creating another star ground system, would be a good starting place.

José, I hope some of this is useful to you. I am not sure what your situation at ICAIC is right now, in terms of access to resources and materials. It sounds like you are doing some "state of the art" upgrades, which is just heartwarming news given all the fine and talented filmmakers you continue to foster.

My colleagues and I are very saddened by the recent hurricane's destruction to your country and all the projects of food sustainability. We wish you all courage and hope in the reconstruction effort.

In solidarity,

datejie green

Audio Engineer
*cultures of women's recordings,
research, information & education
Toronto, CANADA


on 25/10/01 8:10 AM, José Llufrío at llufrio@xxxxxxxxxxxx wrote:

Hello, everybody.

Sorry for any duplicates/cross-posting.

In a posting a couple of month past, at ARSCLIST, Graham Newton replied to
Kurt Nauck:
"Be sure there is a heavy contiguous ground wire available that goes
directly to a
solid earth ground at the electrical entry to the building.  Ground all your
equipment to this."

I am now involved in the design/construction of a sound recording and mixing
studio for one of our production units (animated films).

There's much discussion going on among our engineers, about the correct
impedance for grounding the equipment. Recording and mixing will be mostly
digital, but analog equipment will be eventually used too.

What would be the right way to ground the sound studio?

If the DAWs are networked with the rest of the computers in the building,
should everything be connected to a common ground, or should they have
separate grounding with different impedances?

What is the acceptable impedance for grounding sound equipment?

Is the ground to be independent from the grounding in the electrical mains
feed (transformer chamber belonging to the power company)?

I plead to the many experienced people on the list.

Thanks very much in advance.

José E. Llufrío
Technical Advisor
ICAIC Cuban Film Institute
Havana, Cuba

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