Homebrewed Music

I’ve been touting the Zi8 as a low priced tool for “look at me” YouTube videos because it allows the use of an external mic. It’s usually the case that our preferred framing for a shot moves the camera some distance from the subject. This means that the sound recorded by the camera mic is heavily affected by the sound of the room, and that is rarely a good thing for sound quality.

By separating the mic from the camera, I should be able to position the mic for optimum sound while placing the camera for the visual effect I want. Of course, I can do this wihout an audio input on the camera by a technique called parallel recording, that is, recording on a separate audio system of some kind. The familiar clack of the slate at the start of a movie sequence is used to make it easy to synchronize the picture and sound, and this technique works very well for my homebrewed videos as well. Still it’s very tempting to think that recording directly to the camera is an easier way out, with camera audio every take and every edit lining up without any extra effort.

I’ve been interested in the range of options for attaching a mic to the Zi8, and back in December I went on a little mic shopping binge. Between my storage drawer, Ebay, and Sound Professionals I gathered a collection of mics in a range of prices. But I was struck with a glitch in my Zi8 audio, which required several round trips to attempt repair at the East Coast contract repair depot. Eventually Kodak agreed to replace my camera, but by then I was on a lovely trip to Hawai`i.

Test Design

Now that I’m back I’m ready to offer up some test clips. At first I planned to video a number of brief samples of guitar and vocal, which was very troubling to me. I strongly believe that audio sampling should be done with a single performance and carefully volume matched, in order to reduce the number of variables in the sample. As much as we think otherwise, humans just cannot judge subtle (or even not-so-subtle) differences without careful controls. My aha moment came when I realized that I was only testing audio, not video, so I could use a recorded source to get a repeatable performance. Focusing on audio only also allowed me to upload the much smaller audio clips, so the comparison will be quicker and easier.

For level matching I decided to take the easy way out and simply normalize the files. Normalizing raises the peak of a file to a given level, in this case I chose -3 dBFS. I adjusted levels like this so our ears won’t be fooled by level differences, but these samples hide the differences in the real recording you’ll get if you use one of these mics. So I’m including the original sample as well. Remember that I adjusted the sensitivity of the Zi8 for each mic, so the volume levels are affected by that even in the original, un-normalized samples.

I first created a test recording in Reaper, some slack key guitar naturally. I recorded in mono with an Audio Technica AT4050 in cardioid pattern. Then I added a bit of narration. All camera mics I know about, and many accessory mics as well, are omnidirectional. There are plenty of reasons why an omni is a good choice, but real trickery is required to get a good stereo image with omnis. So I threw in a bit of movement in the stereo field to evaluate channel separation. I arranged the narration and the stereo test ahead of the music and adjusted levels.

I placed all the mics very close to my normal listening position and played back the test recording through my normal monitoring chaing – Echo Audiofire 8, Hafler P3000, Dynaudio BM6p. A Radio Shack SPL meter showed 74 db C weighted at the mic position.

As I mentioned, I adjusted the sensitivity of the Zi8 for each mic. In each case I adjusted the sensitivity to the highest level that did not show any red. I label the default sensitivity as 0, lower sensitivity goes from -1 to -5 and higher goes from +1 to +5. I wound up using the whole range in this comparison.

Test Clips

Here’s the reference recording. It won’t get any cleaner than this.

or download ref.mp3

I used the Zoom H2 as the mic in my first experiments with the Zi8, so I included it in this comparison. It’s also handy because we can record with the H2 and the Zi8 at the same time. Even though the signal in the Zoom was very low and pumped up with a lot of digital gain in the normalization process, it is quite a bit cleaner than the Zi8. I set the Zoom to M Mic Gain because tests have shown that the H setting adds noise. This still resulted in a rather low level, so raising it also raised the noise as well.

or download h2p.mp3
Original versions, no normalization:

or download oh2p.mp3

I used the rear mics on the H2 so I could operate the controls on the front of the unit. As a result the stereo left and right are backwards in both the parallel clip and the Zi8 clip. Here’s the output of the H2 headphone jack recorded on the Zi8 with sensitivity set to -3.

or download h2v.mp3
Original versions, no normalization:

or download oh2v.mp3

If you’re like me you’ve been fooling with recorders for a while, maybe going back to cassette tapes. Perhaps, like me, you have some kind of little mic in a drawer somewhere. My drawer mic is labeled www.reactivesounds.com but the web site is a dead end now. I bought this to use with my minidisc recorder a few years ago. The mic is omni, no cable (requires an female to male extension), and has been repaired with superglue. I used -2 sensitivity for this mic.

or download drawer.mp3
Original versions, no normalization:

or download odrawer.mp3

I’ve used Sound Professionals http://www.soundprofessionals.com/ for these kinds of recording gear for years. I used one of their T-mics for years with my minidisc, but somehow lost it. They still sell a mic with the same model number, SPSM-1, but it doesn’t look much like the mic I remember. I set the Zi8 to -3 sensitivity for this mic.

or download spsm-1.mp3
Original versions, no normalization:

or download ospsm-1.mp3

The SPSM-15 is the least expensive single point stereo mic sold by Sound Professionals. It appears to have a higher low frequency cutoff than the SPSM-1, and/or lower sensitivity. As a result I set the Zi8 sensitivity to -2.

or download spsm-15.mp3
Original versions, no normalization:

or download ospsm-15.mp3

The AudioTechnica AT825 has been a popular single point stereo mic for many years, but was recently discontinued. The replacements are much higher in price, so it might be worth watching for used examples of the AT825 on Ebay or Craigslist. It seemed perfectly matched to the Zi8 and worked well at the default sensitivity setting.

or download at825.mp3
Original versions, no normalization:

or download oat825.mp3

I was impressed with the performance of the AT825. I was very disappointed in the AudioTechnica Pro 24. Although it looks much more impressive than the T-mics from Sound Professionals, it was very low in output, requiring that I set the Zi8 to the maximum +5 sensitivity.

or download atpro24.mp3
Original versions, no normalization:

or download oatpro24.mp3

Let’s Look at the Video

Let’s finish off with some actual video. Be careful with comparisons, but perhaps there will be some blatant differences we can take away. When I framed the shot to include the whole guitar the camera wound up about 5 feet from the instrument. I adjusted the Zi8 sensitivity for each mic using my normal procedure – the highest setting that did not show any red squares.

I had a little fun with my new Edius Neo 2.5 software putting together a compilation of the mic demonstrations.

All these mics sound better here than in the audio test with the recording, but they still show their basic characteristics. The camera mic picks up a lot more room, as it must at that distance. And since the room is a boxy little thing, the recording sounds small and boxy.

The H2 in this clip is very slightly overdriving the Zi8, to my ears. The slightly dark voice of the H2 comes through as well. The Sound Professionals SPSM-15 does a pretty decent job for very small bucks. I failed to mention in the video that the sensitivity on the Zi8 is down to -3. This means the SPSM-15 is quite sensitive, so it might be a problem if your source is loud. To my ear the AT825 is the winner. I like the clear presentation. I’m sorry I didn’t do a better job of balancing the channels.

I hope these comparisons are useful. I plan to try these mics with a different camera in a future post.