Wireless Audio Recording on loca

Wireless Audio Recording on location / Wireless Recording / Recording Audio Wirelessly

This paper describes a system to record multiple tracks of 24 bit audio at up to and including 192 KHz sampling rates using off-the-shelf 802.11G components. This system has been in use for over a year and, compared to systems using audio �snakes,� proven itself to be an enormous set up time saver, provide cleaner more transparent audio, and be down-right fun to use.

After 20 years of recording to Ampex 351s, AG-440s, MR-70s, MM-1100s, Revox A77s, and the Braun tape recorder (the first transport with full logic controls), I began recording to computer in 1991 using an 8 microphone input Yamaha mixer that output to a Turtle Beach 56K interface. The computer was an IBM 286 with a $2000, 1.5 GB Maxtor SCSI I hard drive (that failed after a year, by the way. Maxtor wouldn�t look at it; said it was junk to begin with). Turtle Beach was bought out by a company interested only in selling to gamers and other consumer interests and their professional product fell by the wayside. One valiant programmer posted drivers for the new Windows 95 operating system but they were buggy and of little use. I shifted to a new shareware program called Sound Forge that proved extremely stable and reliable. Over the next few years I switched to Mackie mixers and Lynx and then M-Audio Delta 1010 interfaces. I was locked into a thought pattern that said you use microphones that output to a snake that input to a manual mixer to a set of headphones or monitors and �that�s the way you do it.�

My engineer son, Peter, in the late 90�s began to ask me if I wouldn�t like to have a system where I didn�t have wire strung everywhere and that allowed me to sit anywhere in the audience instead of outside in a truck or backstage or even another room. I told him that would be great but I couldn�t see how that could work. He suggested I get a copy of PCAnywhere and experiment. There was just no way that would work! But, I did begin to think outside the box! Then in 2005 it suddenly became possible.

By this time Peter was a Senior Scientist for Titan (L3) and had moved to Maryland. He provided the concepts while I made them work. I purchased my first laptop using an Intel M processor (They were too mickey-mouse up to this point) and decided after some experimentation that this thing could be used for serious location recording work. The real break-through came when MOTU introduced the Traveler. This unit had microphone pre-amps, converters, amplifiers in a 1U package. But the important feature was that the microphone pre-amps were software controllable! Amazingly MOTU doesn�t even mention this in their advertising but it�s what sets their unit apart from Mackie, M-Audio, Pre-Sonus and others. I found out about it by talking with the guys that design and manufacture the MOTU gear. Aphex does make a mixer with VCAs but it�s only a mixer whereas the MOTU has converters � everything needed for recording. Meanwhile, over in Maryland, Peter was using Windows XP�s Remote Desktop extensively at this point and conceptually put the whole thing together, even suggesting the supporting equipment.

The dirty little secret is that it�s not necessary to record wirelessly. It�s only necessary to control wirelessly! And this is very feasible using Remote Desktop. To give you an idea of what�s involved: I have an 8 space SKB portable rack that I place at the front of a concert hall (or school, church, etc.). It contains, top to bottom, a Furman Line Filter with LED lamps, a 1U chassis with an AES M/S Decoder and Ramsey FM transmitter, two MOTU Travelers, a Marantz PMD 570 (for backup and also has transport controls that are remote controlled), an IBM Netvista computer, and, finally, a 1U power supply chassis (home-brew), that replaces all the wall-warts and contains an Ethernet to serial converter. The rear cover for the SKB rack contains a velcro strap to retain a Linksys WR54TGS 802.11G Router with four way Ethernet switch. Short cable runs from the microphones to the Travelers keep phase shifts and band-pass filtering effects from distorting the audio yielding a sound with greater depth and transparency. The router is placed on top of the rack and connected to the Ethernet connection on the computer and the Ethernet to serial converter that goes to the Marantz PMD-570. This little DHCP network is MAC filtered to allow only the MAC addresses for the converter, IBM computer and my laptop. The IBM goes into hibernation each time it is turned off so no keyboard, mouse, or screen is necessary after the initial setup. I take my laptop, go sit anywhere in the auditorium, and connect wirelessly to my little network.

After executing Remote Desktop, the desktop on the IBM comes up on my laptop and I execute the MOTU CueMix virtual mixer. This gives me full control of the microphone levels, pan, pads, etc in 1 dB steps. I actually have more and better control over my setups than ever before. I know exactly where each mike is set and it�s all there on the screen in front of me. (These setups can be memorized and saved, by the way.) Then I execute the recording program and set it up for the job. Finally, I bring up the transport controls to the PMD-570 backup recorder. It uses one of the four mixes from the MOTU virtual mixer and is capable of only two tracks. One of the other mixes feeds the Ramsey FM transmitter which allows me to monitor anything and everything using a Sony Walkman radio with headphones. While Remote Desktop does have an audio return it is not of sufficient quality to do serious work. This will require 64 bit Windows and the new 802.11n draft systems. (They�re called draft systems because a standard has not been determined at the time this was written. See Addendum below for update on this matter) Other outputs from the mixer allow playback in a recording session or other applications such as a sound system feed or feed to a videographer.

The entire rack, with everything running, consumes about 150 watts. With my Galaxy Far Outlet 300 supply + 100 Amp deep discharge battery I can record for about 3.75 hours. The Far Outlet enables operation from 11-15 VDC or 85 to 260 VAC, 50 or 60 cycle, which is very handy for recording outside the US. Some have asked if I use a UPS. No, I don't because I've found the UPS to be less reliable than the AC mains in the US. However, the Furman filter is extremely valuable. I can think of a church in Little Rock that shut me down twice when the AC came on. The Furman takes out that huge spike and eliminates the problem.

It all works wonderfully and reliably giving me more versatility than I ever dreamed of. I can even check microphones now without having someone tap the stand. I can record using only the IBM. I can still connect using a snake. I can still record from the truck. I can record using the laptop with a 6 foot Firewire cable connecting me to the rack so the recording is actually to the laptop drive. I can record using a length of Ethernet patch cable to connect the laptop and the rack system. Or, I can record wirelessly. The options are many and allow me great freedom in the over 200 location recordings I do in a year. I save hours of setup time or worrying about where to place cables so concert-goers won�t trip over them.

Conceptually, it�s simple enough. The devil is in the details. Even the recording software enters the picture. For example: I love the Sonic Foundry/SONY software and use it for all my work. However, it has a fatal flaw in that the transport controls are not correctly written. If you know anything about RF you know that it is impossible to maintain a 100% reliable path, especially when you�re dealing with digital devices. The digital boys know little about RF and it shows. This means that 802.11x transmissions dropout often just as does a cell phone. When this happens the SONY software also drops out of record and, bingo, you�ve lost the job. I tested many other recording packages before settling on Cubase SE. It�s inexpensive, incredibly reliable and when you put it in record mode it stays there until you take it out. I can start recording, shut down the laptop, go to the restroom, come back, execute Remote Desktop, and re-connect to Cubase which is still recording. Further, when you stop recording in Cubase it stops immediately and can be put into record again instantly. The SONY software and all others tested took extensive time to save each track and then �re-draw� the wave forms. So, I use Cubase to record, then pull the tracks into Vegas and Sound Forge for editing and mastering (to include CD-Text) and CD-Architect for the final product. (SONY indicates no interest in fixing the functional flaw in their software even though I brought it to their attention.)

Hopefully this will whet your appetite and excite your imagination in other ways to think �outside the box.� Pursue it! Recall the doctor that discovered ulcers were usually caused by simple bacteria. The multi-million dollar labs and researchers missed it.

Just so in our business! You don�t need Cobra networks and Cobra enabled equipment. It�s really much simpler than all that!

Addendum: September 8, 2006

I just replaced the Linksys Wireless-G w/Speedbooster Router (WRT54GS) with the new Netgear "N" Router with Gigabit switch (WNR854T) and added the PCMCIA "N" Card (WN511T) to my laptop. The throughput is enormously improved. I'm seeing data rates as high as 300 Mbps vs 54 Mbps with the older Linksys unit. (The Netgear is the only "N" MIMO unit as of this writing that does it right, by the way). The result is much smoother operation using Remote Desktop. I can even play return audio smoothly. However, this requires using Microsoft Sound Mapper or Classic Wave Driver on playback in the remote computer. I am unable to find a way to loop audio from an external breakout box such as the MOTU Traveler or Delta 1010 back to the remote computer audio stream. There is a large lag or latency in the playback anyway so it appears the return audio would not be a good way to monitor after all. Using the Ramsey FM transmitter as described above does away with latency and allows for monitoring of individual microphones, etc. So it's still the best way to go.

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