IN USE
I easily attached the DXA-SLR to the base of my 7D via a threaded bolt, which I was able to snug up by turning a knotched rotary dial just below the top plate from its side. This created a solid bond between the camera and DXA adapter with the LCD screen aligning perfectly with its control panel, yet leaving enough clearance on the right side to enable changing the camera battery (bottom right corner) without having to loosen or detach the two units.
After inserting a fresh 9v battery (not provided) and powering up the DXA-SLR, I connected a self-powered (AA battery) mono mic, Rode’s NTG-2 shotgun. However, in my haste to get started I neglected to insert an AA battery in the mic and thus inadvertently required the DXA’s optional 48v phantom power. I followed the checklist of settings in the compact manual including setting the ground switch to the two setting and the gain switch to high, as prescribed.
I quickly discovered that the DXA operates independently of the DSLR as I began hearing ambient audio in the headphones even before I turned the 7D on. Moreover, I had to dial down the headphone level a bit when recording street scenes and ambient audio on a fairly busy truck route. The perplexing thing was why the green LED, which signifies a strong audio signal (-12 dB) lit up only sporadically, when large passing trucks were accelerating or decelerating close by, despite hearing various fairly loud distinct street sounds in the headphones. In playback (on camera), I confirmed by ear that I had adequate signal strength in the recordings despite the lack of confirmation from the LED signal level display.
To be sure that this wasn’t a microphone issue, I tried three other shotgun mics including the Sennheiser ME 66 a short Sony shotgun and the AT 897 with similar results. In all cases I got very satisfactory recordings, with good strong signals even though the green LED ‘good signal’ light only lit up in response to fairly loud sounds. To me it seemed like the green light threshold was exceptionally high and hence not particularly useful for monitoring audio levels for general-purpose recording.
To test whether the LED green light threshold was set too high I used a Sony PCM D50 portable stereo recorder which displays a full range of signal intensities on its LED panel from -50 to 0 dB and beyond. Moreover, it also momentarily displays the precise dB value of each distinct signal, on the right hand side of its screen. After testing a number of sources from the radio and TV to household sounds like refrigerator motors and flushing toilets, to my surprise, I confirmed that threshold for triggering the DXA’s bright green LED, or ‘good signal’ level was around -12dB, — precisely as described in Beachtek’s Operating Manual for the DXA-SLR. Unfortunately, although the LED is designed to glow red, if over modulated, (above 12 dB.), there is no corresponding color light for audio signals weaker than -12 dB. This leaves the shooter rudderless for gauging the relative intensity of slightly weaker audio signals (below -12 dB) which includes a great deal of perfectly useable, even if somewhat softer audio. This was disorienting for someone like myself accustomed to seeing a full spectrum of audio levels displayed on the VF screen when shooting, from the fairly faint to the loud and clear. Nevertheless, at least I could be confident in knowing that any signal loud enough to trigger the DXA’s green LED was -12 dB or greater, but less than 12 dB. For fainter sounds, I could either trust the DXA to pick up and amplify them somewhat, or use my headphones to roughly gauge their intensity. I used the latter especially when recording nat sound, including many species of birds and small mammals. I actually became fairly accurate at gauging relative signal intensity by ear, using the headphones by always keeping the volume dial set at the mid-point. Hence I grew accustomed to using my ear to recognize whether a given sound was louder or softer than the -12 dB sweet spot on the DXA, which triggers its LED “good signal” green light.
To further enhance audio quality (versus quantity) whenever possible, I used the “auto gain disable function,” which streamlined the often erratic fluctuations in audio level inherent with auto-gain, which generally netted cleaner, even if slightly weaker, audio recordings with little or no hiss.
While I did a brief test in “line mode,” otherwise, all recordings were done in “mic mode,” mainly in mono, for the sake of mobility and for the convenience of mounting and handling only one mic versus two. However, I also tested Audio Technica’s BP 4029 stereo shotgun mic, which proved to be an ideal length and weight to mount on the 7D’s accessory shoe or that of the Frezzi support arm attached to the base of the DXA-SLR and camera. Once again the level of the audio recorded appeared to be “in the zone,” despite rarely triggering the green LED signal level indicator even though I heard often heard “clean audio” loud and clear in the headphones (with volume set at the mid-point).
THOUGHTS
Beachtek’s DXA-SLR is a major leap forward in closing the gap between the current generation of DSLRs and professional video camcorders in terms of audio recording. It is essentially a very compact mixer with pre-amp, which docks easily and unobtrusively to the base of most DSLRs to enable a full range of pro audio functions for simultaneous recording to the DSLR. This includes the use of most pro-microphones — with or without phantom power, both stereo and mono types. Moreover, the DXA-SLR even makes it possible to enhance the audio quality achievable with (mono) mics with single 1/8” mini-plugs. The difficulty of monitoring recording levels easily and reliably using the simple threshold triggered bi-colored LED indicator light is probably its greatest limitation. While this is inconvenient, it does not preclude consistently high-quality audio recording with the Canon 7D or other DSLRs, with or without the auto gain option. Considering its moderate price and overall functionality, the DXA-SLR is a compelling and affordable ($399) audio solution for the audio-minded pro-DSLR shooter. Moreover, thanks to its thoughtful design, it doesn’t impede other mounting options or battery changes with a Canon7D or (presumably) with other professional DSLRs for HD capture.
Beachtek DXA-SLR Adapter
http://www.dv.com
By Carl Mrozek
http://www.beachtek.com/
dvideo@hol.gr
