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director of photography, peter gray, dp, cinematography, dop, cinematographers, lighting cameraman, videographers, dv, high definition, 24p, digital films, HDW-F900, CineAlta, Varicam, AJ-HDC27F, Viper, 70mm, independent films, lighting directors, filmmakers, filmmaking, HDW-700AHD AUDIO MONITORING
I've been canvassing opinion from sound mixers and audio rental facilities based on real-life production experience regarding the 5-pin XLR audio monitoring output on the Sony F900 HDCAM and HDCA-901 Adapter. I believe this information is equally applicable to the Panasonic HD Varicam and the Panasonic AJ-SDX900 camcorders. Based on these comments and feedback, I've drawn up these schematics, or Quick Reference Guides, below. These guides are really works in progress, and therefore may change with additional feedback from audio professionals working in the field. With the Sony CineAlta HDW-F900 camcorder, the 5-pin output socket can be set up to monitor tracks 1 and 2, or alternatively to monitor tracks 3 and 4. This option is selected in the F900's Maintenance Menu #8 called < VTR SETUP >. Go to the second item, PB (PLAYBACK) AUDIO CH(ANNEL), and select "1/2" or "3/4". Sony provides a second 5-pin monitoring output from their HDCA-901 Adapter back where you can monitor tracks 3 and 4. So it is possible to monitor all four tracks from the camera simultaneously, using the two 5-pin audio outputs at the same time.
One of the biggest issues with monitoring High Definition audio is dealing with Audio Ground Loop problems. Where the ground or chassis potential is made common between different pieces of equipment, there should only be one electrical path between linked equipment. It is important to eliminated multiple paths or parallel connections, otherwise various types of audible interference can be added to the signal making precise monitoring difficult, or even impossible. More often than not, the regular AC ground path provides a secondary, parallel connection leading to this problem. So it is a good practice to make sure all audio grounds are isolated (or lifted). The use of Audio Isolation Transformers in conjunction with Ground Lift Switches is often necessary to control these annoying ground loop problems. If you elect not to do it the correct or "proper way" with Audio Isolation Transformers, then you need to be aware of the pitfalls with taking shortcuts with simple adapter cables (like those shown here). I'm finding different sound professionals using different wiring configurations that work for their own particular application/s. So there are no absolutes, and no definitive approaches with wiring adapters. So what I've done here is to try and distill a general approach in these guides that is likely to be the most universally successful. I've found the various approaches to the "best" wiring configuration is all about different ways to deal with these audio ground loop issues. Every real-life production scenario tends to be different in terms of ground loops, so the individual approaches to eliminating these problems tends to be wide ranging as well.
As the F900 monitoring socket provides a line-level audio output, it is not suitable to monitor the audio signal with headphones (although some types of headphones will work better than others). It is really designed to output an audio signal to some sort of monitoring amplifier, like in a mixing panel. You need a mixer with 2 mono returns (or inputs for an external audio deck). The use of a isolation transformer at the mixer input is highly recommended to eliminate ground loop problems, for example, the JENSEN ISO-MAX model PI-2XX (see details below).
The use of Audio Isolation-Transformers in conjunction with Ground Lift Switches is often necessary to control those annoying ground loop problems. I've been advised that the best unit to consider is the JENSEN ISO-MAX model PI-2XX Stereo Audio Input Isolator (list price $209-95). The switches on the bottom are set according to the characteristics of the equipment the device is connected to. The 51 Ohm and 10nF series networks are RF damping networks. They provide a termination impedance for the cable shield at high frequencies to prevent any high Q resonances that might aggravate RF pickup. At low frequencies they are high impedance to prevent any circulating AC ground currents (according to Dale Roche - Project Engineer). Each unit handles two channels of audio. See the company's web site: http://www.jensen-transformers.com/pi2xx.html for more information.
For straight headphone monitoring without a mixer, the Sound Devices model HX-3 battery-powered Headphone Distribution Amplifier is worth serious consideration (list $330). It has 2 electronically balanced XLR inputs and 3 headphone outputs (with Mono/Stereo switches). The output is loud, and is very good for monitoring purposes, even on noisy sets. See the company's web site: http://www.sounddevices.com/products/hx3master.htm for further information. This is the correct professional way to use the 5-pin XLR as a headphone monitoring output. Other approaches are prone to a range of problems that will degrade the quality of the audio being monitored, perhaps seriously. I'd appreciate any comments or feedback regarding the presentation and accuracy of this (evolving) material - thank you. By the way, if you e-mail me, I can send you these schematics as Adobe Acrobat (".pdf") files, which are better suited to printing. The file size is very small (8 to 14KB) and they produce very clean copies if a 'hard copy' print out is required. Reference: Sound Devices, LLC
Peter Gray
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