Xacti Audio Input

The Problem

The ability to publish and watch HD video easily has really inspired me to make better use of video and audio to demonstrate things I’m working on. Although I’ve made videos for YouTube before, they were always produced in a rather round-about way using a digital still camera in movie mode, and then synchronizing externally recorded audio. This process takes a long time and the results aren’t all that amazing. Some major problems (as of 2010) with digital still cameras for video recording are a lack of real-time zoom, focus and exposure controls. Just like a still picture, once you lock the exposure, that’s what you get for the entire recording.

Another problem is the audio. Digital cameras have terrible microphones and it’s almost completely necessary to record and mix separate audio and then re-sync it with the video sometime during the editing process. This takes a lot of extra time and is a hassle. Finally, most digital cameras that I’ve used make MJPEG video, which is technically quite great, but in reality is really large and cumbersome to deal with. When shooting at 720p, a 4GB card gets full in a matter of minutes. This makes the projects on the computer very large, and takes a long time to move files around.

So in my quest for a simple, high quality way to record and produce good video for the web, I set out to find a camera that would have: HD recording, solid state memory, a mic or line input for supplying my own audio, and h.264 compression or some reasonably compact movie format. Well, as it turns out there are quite a number of HD cameras on the market, but almost none of them have audio line or mic inputs. The ones that do cost over $700. This used to be a feature on every camcorder, but it seems as though a $0.10 part is now being deemed a premium feature.

My first choice was a bad one. I decided to try the Canon FS200. It’s a $250 SD camcorder with a mic input that records to SDHC memory. I figured, perhaps 480 lines is enough, since most people on YouTube probably watch the videos at that resolution or lower. But what I didn’t realize is that SD doesn’t mean 640×480… it means NTSC. So all the colour problems and softness of this antiquated video format show up in the recording.  My cheap digital camera’s movie mode does a much better job. Sure it’s nice to have power zoom, a hand strap and all the usual camcorder features, but not at the price of terrible video quality. Although I was able to interface with the mic input from my mixing board (more on that later) the picture just didn’t impress me enough to keep it. I returned the camera the next day and continued my quest.

The Solution

After doing some more research and checking out what local vendors were selling, I came to the conclusion that the best bang-for-buck in HD camcorders was the Xacti line by Sanyo. I liked the interesting pistol-grip form factor. This seems like a design decision to justify having a large optical section. After looking at the Flip and other pocket camcorders, it was clear that a real lens assembly with zoom and autofocus was the only practical way to get good images. A fixed lens with no macro seems like a really bad idea. And demo videos on YouTube confirm that.

The model I got was the Sanyo Xacti VPC-CG10 for $269… only $20 more than the SD camera I returned. Unfortunately it doesn’t have a mic input. I mainly chose this camera based on price and picture quality, but also because the mics are on the flip-out LCD screen. This seemed much easier to hack, and avoided any disassembly that might put the lens and camera module at risk.

As you can see in the photo, the mics are mounted in little rubber holders. Their wires are conveniently accessible through holes in the metal shield. To test the audio input I scoped around and found the correct audio wires. By injecting some audio into the correct pins (through a coupling capacitor) I was able to record some sound.

Next I disconnected the internal mics and connected a 1/8″ female cable to the pins, and tacked the ground nearby. I figured whatever coupling I needed to do would be done externally. Since the mic pins also  provide bias voltage for small electret mics, it would be useful to have this voltage available outside the unit. Only a small notch had  to be carved in the end of the screen housing for the cable to exit. The cable coming out of the side of the screen doesn’t look awesome, but I certainly don’t mind it.

Audio Coupler Box

You can’t just feed line-level audio into the mic input. First of all there is a bias voltage (about 2V on this camera) on the mic pins that is used to power the internal electret mic capsules. Also, the level of the audio signal needs to be quite low. I found that while speaking loudly near the mics on the Xacti camera the level peaked at around 50mV peak. This means that normal audio levels are probably in the range of only several millivolts. I built a little coupler box that can be attached to a pair of either a balanced or unbalanced 1/4″ outputs and couples the signal to the camera through a 25′ cable.

At first I was hoping that I could feed stereo audio into the camera, but was disappointed to find that there is some sort of noise reduction technique going on between the two microphones. Feeding in stereo sound, especially things like reverb make for very strange recordings. Another problem I noticed was that most recorded sounds had a sort of burbling quality to them. I struggled with this for a while thinking that maybe my audio level was wrong and I was hearing MPEG artifacts. Eventually I found that the Wind Noise Reduction setting in the camera needs to be on. Without it, the sound is terrible even with the internal microphones. This feels like a bug to me… perhaps the straight (non-noise reduced) signal path was never really tested, since the setting is on by default. I turned it off because I specifically thought it would cause problems.

Conclusion

You can decide for yourself. Check out the video below. I find that the audio isn’t wonderful, but it’s more or less useful. If you want to record speech from a good mic and have it be in sync with the video, than this setup works fine. If you want stereo sound or better quality audio to use during editing, perhaps an external recorder would be more useful. I have a feeling that I will use a bit of both. But having an HD camera with mic input for less than $300 feels like a big win. I’m not so sure that an extra $400 or more for a camera with a mic jack would really give me all that much better results.