chapter 15 Sound for production 343 Figure 15-21 Digital audio tape recorders (DATs) record to a proprietary audio cassette (left), and DVD-RAM media like the Fostex PD6 (right) make random access possible. digital audiotape and dVd-raM Digital audiotape (DAT for short, or R-DAT for rotary head digital audiotape) is an audio- only cassette format that uses a magnetic tape 3.81 mm wide and that writes its data in a helical scan pattern with a flying record head--much like a DV video camera. Professional DAT recorders have a frequency response around 20 Hz to 22 kHz and the signal-to-noise ratio is outstanding at around 90 + dB. The drawback to DAT machines is their fragility in the field. They seem especially vulnerable to dust and humidity and can jam up in extreme conditions. The other drawback is their linearity--meaning that one needs to fast-forward or rewind to find sound takes, rather than access them through the instantaneous random access of hard drives and other recording formats. The DAT format is quickly phasing out in favor of digital recorders with no moving parts. Industry reports indicate that there are no new DAT recorder models in the pipeline, but since many production companies and film schools have invested in these machines, they will remain in circulation for a while longer. DVD-RAM recorders function similarly to hard disk recorders. DVD-RAMs write the audio data in concentric tracks (like hard drives) instead of one long spiral track (like DVD+R and ­R, which are entirely different formats). DVD-RAM does not need DVD burning soft- ware and, using a DVD-RAM reader, they can be loaded and read instantly on any PC or Mac computer system. (Figure 15-21). sound recording on dV camcorders As I mentioned earlier, for narrative filmmaking it's usually a good idea to go with double system sound recording, even when shooting DV, which has the capacity to record audio (see page 336). But if you have no choice but to shoot single system sound with your cam- corder, you can still get great audio. DV camcorders that use tape as their record medium write PCM digital audio along a helical scan with a flying head and file-based media (P2 and SxS) create sound files (see page 208), and this audio is already in sync when you sit down to edit your footage. Most camcorders of any quality have high recording specifica- tions: 48 kHz and 16 bit. In theory, these are great audio specifications; however, as we've discussed before, there are other factors that contribute to audio quality. Miniplug audio inputs are especially a problem with low-end DV camcorders. The con- nections are fragile and prone to poor contacts, and miniplugs are unshielded and unbal- anced. Many people use an XLR-to-mini adaptor (called a pigtail) so that they can use professional external microphones. This, of course, is better than nothing, but the problem with this solution is that it converts your lovely balanced, shielded audio into an unbal- anced signal, vulnerable to interference and noise. A few years ago I was shooting a short film on DV and using a professional microphone connected to the camera with an XLR-to- mini adaptor. After a few takes into our shooting, the sound recordist noticed that we were picking up a Top-40 radio station. When we played back the tape we could hear it. It was very faint, but sure enough, there was Britney Spears leaking onto my audio track!