Quick VX2000 Audio Test Results

Further to the previous post on the audio performance of the VX2000, a quick and simple test was carried out to establish some data. A Sennheiser K6 microphone was connected to the camera (battery powered obviously as the VX provides no phantom power option), and held approx. 30cm from the subject. The gain on the camera was set to manual mode and set to its minimum position. Then, with the camera set to record, a simple count, at normal conversation level, was spoken into the microphone. This was repeated with the manual gain set to 2 clicks up, 4 clicks up, 6 clicks up and finally 8 clicks up, which resulted in clipping (i.e. hitting or surpassing the 0dBFS level on the camera).

The camera was then connected to a laptop PC via Firewire and the audio "footage" was captured into Premiere Pro. It was obviously important to use a digital transfer into the PC so as not to add any gain or attenuation to the signal. The audio was then exported as a wave file using standard DV settings (fs=48kHz and bit depth = 16) and then loaded into Sony Soundforge 7. The signal was monitored from the PC on a pair of Beyer DT100 headphones connected to an Edirol UA25 audio interface and immediately upon playback it was noticeable just how much hiss there was on the recording, even with the gain in its minimum position. The files were approximately analysed by observing the peak levels on the dBFS meters within Soundforge for both the noise floor and for the recorded speech for each of the gain settings; the results are shown here:

0 clicks:
Noise floor: approx. -49.5dBFS
Peak of recording: approx. -11dBFS
Approximate S/N Ratio: 38.5dB

2 clicks:
Noise floor: approx. -43.8dBFS
Peak of recording: approx. -11dBFS
Approximate S/N Ratio: 31.8dB

4 clicks:
Noise floor: approx. -40.6dBFS
Peak of recording: approx. -7.1dBFS
Approximate S/N Ratio: 33.5dB

6 clicks:
Noise floor: approx. -36.8dBFS
Peak of recording: approx. -2.1dBFS
Approximate S/N Ratio: 34.7dB

8 clicks:
Noise floor: approx. -39dBFS
Peak of recording: approx. 0dBFS (and above)
Approximate S/N Ratio: 39dB

Observations and Conclusions:
It is important to note that these are approximate measurements and that the room used to carry out the recordings in was not acoustically treated in any way. Therefore, the background noise level was fairly high and factors such as traffic noise from the nearby road needs to be taken into account. However, audibly, the noise floor was very high on all settings resulting in a poor S/N ratio. There was also some occasional low level clicks and pops throughout the recordings too. It is also interesting to note that the approximate S/N Ratio hardly changed regardless of manual gain position on the camera, therefore one would suggest that when using this camera to record audio with, perhaps a low gain setting is equally as good as a high one? Peaking a low as -11dBFS is fine when recording DV audio (as already discussed elsewhere, some texts state that DV audio can peak as low as -20dBFS to allow for 20dB headroom), and the audio file could always be normalised to bring the peak level up in the edit any way. Whatever the gain position, the recording quality is compromised by the high noise levels which isn't masked particularly well by the signal.

Some further articles of interest are:
http://www.dvfreelancer.com/articles/vx2000.html

http://www.gregjwinter.com/compare.htm