Re: inexpensive recording technology (mup1dm )

Subject: Re: inexpensive recording technology
From:    mup1dm  <mup1dm(at)SURREY.AC.UK>
Date:    Tue, 16 Jan 2001 11:14:03 +0000

There are several facets to consider in making a recording for subsequent analysis. One aspect is the sound level recorded onto the tape. The voice needs to be loud enough that it overcomes the inherent noise of the tape (or whatever) but not so high that it distorts. In practice, this generally requires someone setting a knob. Inexpensive recorders have "automatic level control" that will reduce the level of loud sounds and raise the level of soft sounds to keep everything within the acceptable range of the recorder, but these tend to give recordings that have background noise intruding wherever the voice level is soft. Cassette recorders such as the Marantz PMD series portables and the Sony "pro walkman" recorders (the latter generally available from J&R Music World in NYC) are good quality cassette recorders and also have level controls. The cheapest Marantz starts at about $240, however, and it can be difficult to find where they are sold. (Try the pro-audio supplier Full Compass, at (800) 356 5844) (Madison Wisconsin) Another aspect is extraneous noise. The recorder itself makes noise, so a mic attached to the recorder is usually not a good idea as the sound will carry through the plastic to the mic directly. So a recorder with a jack for an external mic is best. This also allows the recordist to get the mic close to the mouth of the person talking, which helps to get a much better ratio of voice to everything else. Noise from mic handling can also be a problem, so either use a mic that is securely fastened to the talker (headworn or lavelier) or a handheld mic that has "professional" caharacteristics -- purchase it from a music store or pro-audio supplier and have them make a cable to adapt it to your recorder. This brings up the fact that some mics have a funny characteristic that the tonal balance changes with distance from the sound source -- you get more bass as the mic gets closer to the lips. If the ratio of fo level to other frequencies is important in the analysis, then you should stick to an "omnidirectional" mic, which will not have this characteristic, rather than an "unidirectional", "shotgun", "cardioid" or other "pressure gradient" mic that will. Cassettes are inherently unstable in pitch. If you record a pure tone of fixed frequency on a cassette it will play back with warble (frequency modulation). If you play it back on a different player, you are unlikely to get the same frequency at all. A digital recording will be easier to analyse. DAT recorders (digital audio tape) are probably the best portable digital recorders, but starting price is in the range of $600. Mini-disk recorders are much cheaper, but may be a very poor choice for subsequent analysis, because in a physical sense the recording is very noisy -- they sound good because the noise is placed in time and frequency in such a way that it is masked by the human auditory system. While the noise may not be particularly audible to us, it might be a problem for analysis equipent. If a researcher will be carrying a laptop computer anyway, then the best quality answer for the least money might be to use any inherent sound capability on the computer to make the recording. Save disk space by recording monaural sound files at a low (e.g.: 22000hz 22 kHz) sampling rate, *without* compressing to MP3 or whatever. Save more space by using PKZIP or Stuffit to reduce the file size after the fact. A headworn computer mic will always give decent quality sound if the input levels are set correctly. If pitch and automatic level control are not going to cause a problem in the analysis, then a good ald-fashioned $30 mono cassette recorder of the type we used to use in classrooms in the '70's will be just fine if a good microphone is used. Douglas McKinnie University of Surrey

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Electrical Engineering Dept., Columbia University