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SoundField SPS200 Stereo/Surround Microphone System by Bruce Bartlett The SPS200 Software Controlled Microphone offers very clean sound and user-friendly software processing at a great price. This portable, lightweight (220g) unit is a coincident stereo/surround microphone from SoundField costing only $2700. The SPS200 compares very favorably with the more expensive microphones in the SoundField range, all of which use a hardware processor. Some applications include stereo or surround recordings and broadcasts for electronic news gathering, documentaries, musical groups, sound effects, sporting events, environmental sounds, and ambience. You can feed the mic signals easily into a laptop recording system or studio DAW. Powered by standard 48V phantom power, the mic includes four low-noise, studio-grade, cardioid condenser capsules. A breakout cable provides the four mic-capsule signals (A-format) on balanced XLR connectors, which you plug into four identical mic preamps or an audio interface with mic pre's. Several FireWire interfaces have four or more mic preamps, such as the MOTU Traveller, the Focusrite Saffire Pro, PreSonus FireStudio and the Prism Orpheus. All can transfer the four A-format signals from the SPS200 to a DAW. You can also connect the SPS200 to portable multitrack recorders with phantom-powered mic inputs. Included with the mic is SPS200 Surround Zone software, which lets you create mono, stereo or surround audio from the original A-format capsule signals. You can "steer" and "zoom" the microphone, and change its pickup pattern, after the recording is done. This software is available both as a Pro-Tools TDM plug-in and a VST plug-in for both Mac and PC DAW hosts. Also included is a rugged carrying case (Figure 1) with a mic cable, mic holder, Surround Zone software and owner's manual. The heavy duty 5 meter cable has a screw-lock 10-pin connector and four XLRs which are color-coded and labeled Left Front - LF, Right Front - RF, Left Back - LB, and Right Back - RB. Make sure to plug them into your recorder in that order. Some useful accessories for the mic are camera hot-shoe adapters and the HW4000 shock mount constructed of curved, springy wires. Both are available at www.soundfield.com. The SPS200 Zephyx kit includes a short-body mic -- SPS200- SB, which is an SPS200 modified by DCaudiovisual -- fitted into a Cinela Zephyx suspension mount. See Figure 2. From the SoundField website you can order a dual-layer fabric windscreen or fur windjammer which covers the Zephyx mount. Figure 2. The Zephyx grille surrounds the mic and Figure 1. Carrying case and accessories. holds a fabric or fur cover to keep out wind noise. 1. In Figure 3, consultant Gary Pillon demos his Pillon Virtual Array (PVA) camera rig, which holds a Format Agnostic HD, 3D or film camera, lights, and surround micropohone. The eagerly awaited 4 Vario harness will actually hold systems up to 40 pounds in this manner. This assembly is effortless to carry and easy to handle in the field. In Figure 4, Joel Porter, audio instructor for Lifton Institute for Media Studies, tries the PVA. The SPS200/Zephyx feeds their Sound Devices 788T recorder, clamped to Gary's Turtle X Strong Vest. Figure 3. Gary Pillon with his HD Figure 4. Joel Porter recording the SPS200 to a camera/SPS200 rig. Sound Devices 788T 8-channel portable HD recorder. Manufacturer's specifications for each mic capsule are listed below: Frequency Response: 40Hz-20KHz Sensitivity: 14mV/Pa Signal to Noise Ratio (DIN/IEC): 82dB Equivalent SPL (DIN/IEC): 12dB Maximum SPL :130dB HOW IT WORKS The SPS200 is a SoundField system, which utilizes a patented four-capsule microphone and decoding software. On the top of the mic are four cardioid electret-condenser capsules about 3/4" diameter mounted 90 degrees apart (Figure 5). The capsule grilles define the faces of a tetrahedron. Below the capsules is a handle with a plug-in cable, which lets you connect the mic to a multitrack recorder of your choice. The signals coming directly from the four capsules are called A-format. While these signals are not usable as they are, they feed into the supplied processing software which creates a four-channel signal called the SoundField B-Format. Those four channels are known as: X (front-back) Y (left-right) Z (up-down) W (omnidirectional, a reference for the other three channels). Figure 5. SPS200 Surround Microphone. 2. The X, Y and Z channels are effectively three figure-eight patterns at right angles to each other. By summing and differencing those B-format channels in varying amounts, the processing software can create a wide variety of mono, stereo, mid-side, or surround polar patterns -- even in post-producton after the 4-channel recording has been made. Surround formats include 5.1, 6.1 and 7.1; speakers in a square, and speakers in an octagon. Almost any speaker arrangement can be user-defined. Although the capsule diaphragms are separated by just over an inch, the processing results in phase-coherent signals, as if the capsules occupied the same point in space. The four B-format channels capture the 3-D sound field all around the microphone as picked up at a single point. These signals can sum to mono with no phase cancellations. The processing also equalizes the capsule signals to give them a wide, flat frequency response. So you start with a four-channel recording of the mic-capsule signals. Then using the processing software in post, you can effectively point or steer the "effective" or "virtual" microphone(s) as desired. The software allows you to model essentially any number of coincident first-order microphones, each pointing at any arbitary angle and each having an independent pickup pattern. For example, suppose you set the software to create a virtual figure-eight mic. As you move a slider in the software to turn the virtual mic off-axis, you can hear the recorded source become more distant as the null of the figure-eight pattern sweeps toward the source. Or suppose you create a virtual Blumlein array of two figure-eights angled 90 degrees apart. As the sound source moves from center to 45 degrees to the right, you hear the sound image move the same way to the right monitor speaker. When the source moves beyond 45 degrees, you hear the sound imaging becoming out-of-phase and diffuse, just as you would with a real Blumlein pair. It's as if you had a mono mic, stereo mic, or surround mic that could be rotated, tilted, or zoomed at will -- after the recording is made. SOFTWARE Surround Zone software is necessary to decode the four mic signals into usable polar patterns and stereo/surround formats (Figure 6). This software is available for download at www.soundfield.com and is included with the microphone. It has beautifully designed GUI which makes the functions obvious to the user. Figure 6. Surround Zone surround GUI. 3. Surround Zone Software Features • Realtime monitoring of stereo and surround. • Rotate: Allows full 360° simulated rotation of the sound field. • Tilt: Provides ±45° simulated tilt of the sound field. • Zoom: Gives the effect of zooming in or out from the sound source. • End Fire: Re-orients the mic software for end-addressed use as opposed to the standard side-addressed use. • Invert: Maintains correct three-dimensional perspective in both surround and stereo when the microphone is suspended upside down above the sound source. Surround • Six different surround modes are provided: three 5.1 presets, a 6.1 , a 7.1 and an 8-channel preset. • Variable front and rear stereo width control. • Variable rear polar patterns. Stereo • Variable polar patterns. • Variable stereo width. • Variable high pass filter. • Mid/Side encoder. Figure 7 is a screen capture of Cakewalk Sonar Producer DAW software set up for use with the SPS200 The four A- format mic signals are on tracks 1, 2, 3, and 4. Those four tracks feed into a multichannel track 5, which contains the Surround Zone VST plugin. Track 5 would be soloed so you hear only the decoded signal (the virtual microphones). Each mic capsule's signal is recorded on a separate track in Sonar, so you have a 4-track recording of the A-format signals. Here are the control settings in Sonar: 1. Set up a surround bus and insert the software as a VST plugin in that bus. 2. Route the four A-format signals (the four track outputs) to that surround bus. 3. Using Sonar's surround panners, pan the LF capsule signal to LF, pan the RF capsule signal to RF, pan the LB capsule signal to LB, and pan the RB capsule signal to RB. 4. In the Surround Zone software, select the Stereo tab if you want to listen in stereo. If the mic is end-addressed, enable "End Fire". Figure 7. Cakewalk Sonar Producer DAW software set up for use with the SPS200. 4. Figure 8 shows Surround Zone's Stereo window opened in Sonar. Figure 8. Surround Zone software plug-in. The Stereo Angle control lets you set the angle between the coincident stereo pair either ‘live’ or after the recording has taken place. You might use a small stereo angle for a soloist, or use a wide angle to create a wide stereo stage for an orchestra. Stereo angle also controls the effective amount of zoom: the direct/reverb ratio in the monitored audio. The Polar Pattern control sets the polar patterns of the stereo pair, anywhere from Omni through Sub-Cardioid, Cardioid, Hyper-Cardioid to Figure-eight. As you go from omni to figure-eight, the highs start to roll off slightly. Polar patterns and Stereo Angle are displayed in real-time. Most users should find this interface to be very intuitive. Press the Mid-Side button to M/S encode the stereo outputs: Left becomes Mid and Right becomes Side. IN USE You must connect all four XLRs to phantom-powered inputs; they don't work one-at-a-time. All four channel gains (not signal levels) must be identical for correct decoding and all mic inputs should use identical pads, polarity switches and low-cut switches. In the Surround Zone software, be sure to select how the microphone is facing before you decode your recording: side- fire or end-fire, and right-side-up or inverted. Once you are satisfied with the mono pickup, open the microphone signals to stereo. Set the Polar Pattern to what you think will be a good starting point, then adjust the Stereo Angle control for your desired stage width. I used the SPS200 to record a speech walkaround and an old-time string band with the mic facing the group. The mic fed a PreSonus FireStudio audio interface and a computer running Cakewalk Sonar Producer DAW software. Overall, the sound quality of the SPS200 was excellent. Image focus and placement sounded natural. Localization was precise and ambience was detailed. I heard clean, clear sound, a full low end, a very smooth high end, and no audible noise or distortion. Movement of images across the stereo stage was uniform. Gary Pillon walked around with the mic in his HD camera rig while recording, and we heard no vibrations picked up by the mic. Its shock mount works quite well. For all its sophistication, the microphone is extremely light. According to Pillon, "It is as easy to use as a well-built mono shotgun. It will go on any mount that provides a way to screw a 3/8" bolt through it (with a bracket) or on it (with a stud). It keeps the mystique and flexibility of Ambisonic recording while being unusually practical." 5. Pillon cautions, "One of the biggest frustrations in location recording is an accidental change in the speed reference on either picture or sound (even by 0.1%). Digital gear just doesn't like it. Furthermore, CD music is based on a 44.1kHz format, while TV audio releases at 48kHz. For your peace of mind and to avoid expensive problems, make sure to test the system from your shooter and sound person thru editing and audio post." The SPS200 surround microphone is an example of state-of-the-art recording technology, and is very good value. I highly recommend it for pros who want to capture top-quality sound in the field. CONTACTS In the USA: Transamerica Audio Group, Inc., 7320 Smoke Ranch Road Suite G, Las Vegas Nevada 89118. Tel 702-365- 5155, fax 702-365-5145. Contact Brad Lunde / Richard Bowman, email: email@example.com, web: www.transaudiogroup.com. In England: SoundField Ltd., Charlotte Street Business Centre, Charlotte Street, Wakefield, West Yorkshire WF1 1UH ENGLAND. Tel: +44 (0) 1924 201089. Fax: +44 (0) 1924 290460. email: firstname.lastname@example.org. Web site www.soundfield.com --------------------------------- AES and Syn Aud Con member Bruce Bartlett is an audio journalist, recording engineer and microphone engineer (www.bartlettmics.com). His latest books are "Practical Recording Techniques 5th Edition" and "Recording Music On Location." 6.