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Alan, Does everything you shared here apply equally to Mac and non-Mac users. I am a Mac user. Sally >DIGITAL AUDIO > >Going digital gets rid of the noise inherent in using tape. However, if you >are going digital, there are several issues you should consider that will >impact audio quality: sampling frequency, resolution, compression. > >If you want to capture a frequency accurately then you need to have a >sampling frequency that is at least double. The limit of human hearing is >around 20KHz hence the sampling rate on CD quality audio is 44.1kHz. (If you >want to know more about this do a Google search for "Nyquist frequency"). >But, assuming you are not interviewing opera stars who will give impromptu >performances during the interview, you don't care about recording the entire >range of frequencies that the human ear can hear. Normal speech frequencies >are in the mid-range i.e 250 Hz to 8kHz. If you are just interested in >speech you probably don't want the low frequencies or high frequencies >outside this range. If you are recording speech for transcription the low or >high frequency stuff is just noise and it will impact the intelligibility of >the speech you are recording. In previous posts when people mentioned noise >reduction all they mean is that the microphone isn't sensitive to >frequencies at the upper and lower ends or the recorder doesn't encode those >frequencies. You can also get this kind of effect after the fact by using an >audio editing program like Audacity that can be used to filter out entire >frequency bands. Given the Nyquist issue, this means one probably should use >a sampling frequency of at least 16kHz for the best quality. I use 22.05kHz. >Now you can get away with less. Telephone systems generally limit >frequencies to the most critical frequencies for intelligibility, usually >400Hz and 3.4kHz. Similarly with a lot of digital voice recorders--you'll >find many have fairly low sampling rates and will only be good at recording >frequencies up to 3kHz or 5kHz. Personally, if you are going to listen to >this material over and over or transcribe it, I'd want more than the minimum >quality for intelligibility. > >Practically all digital recorders use at least 16 bits to encode audio (i.e. >the resolution, the value that can be given to each sample). I would avoid 8 >bit. The devices that plug into the iPod are 8 bit. It may get the job done >but don't expect wonders. > >Compression is another issue. Uncompressed audio (PCM) takes up a lot of >space. So people use codecs like MP3, ATRAC (what Minidisc uses) etc. to >compress the audio. If you are a linguist you might desire to use >uncompressed audio but MP3, ATRAC, WMA, OGG and other popular codecs will >work very well at encoding speech even at fairly high compression ratios. >The sample rate and resolution are generally more important considerations. > >MICROPHONES > >You probably want an omnidirectional microphone as those are the easiest to >use for this type of work. Some mics are designed for recording speech, i.e. >have a frequency sensitivity geared to the mid-range. You'll also find >boundary or pressure zone microphones that are good for recording meetings >and other events where the mic can be positioned on a large flat surface. >These boost direct sound waves by 6db over reflected sound waves and thus >aid intelligibility in situations where there might be a lot of reflected >sound from walls and other surfaces. In some situations using multiple mics >and stereo recording might prove very helpful. > >TECHNIQUE > >The number one key to intelligibility regardless of what you are using is to >make sure that the speech you are recording is at least 30db louder than any >background sounds or noise (40-50db is better) while avoiding 'clipping'. >Microphones by themselves won't perform miracles in this regard. Lots of >microphones will work reasonably well. What's important is that you get the >microphone reasonably close to the speaker or speakers. Every time you >double the distance of the microphone from the source you drop the audio >relative to background noise by 6db. Move the microphone far enough away >(and it doesn't have to be very far) and the speech you are recording will >sink into the sludge of background noise. And you'd be surprised how much >noise there is in a 'quiet' room. A previous poster suggested lapel mics. >Good idea if they aren't perceived as intrusive and you don't run into a >clothes noise issue. The other strategy is to limit ambient noise as much as >possible. > >RECORDERS > >Voice Recorders ($200-$300). Some new models have much better sample rates >and record in formats that can be readily used by many types of software. >Check out the newest Olympus models (DM-10, DM-20, DS-2200). They have a >best quality mode that samples at 44.1kHz, has a frequency sensitivity of >300 to 8,000 Hz, and encode in WMA. > >Minidisc ($200-$400). New Hi-MD models will record in ATRAC at various >compression ratios as well as PCM. You'll get 44.1 kHZ, 16 bit, stereo >quality audio. Very good quality audio. Downside is that Sony still hasn't >allowed rapid transfer to PC in a format that can be unlocked. Apparently >they will release some type of converter that will allow this in the fall. >As a previous poster pointed out, if you are going to a remote location MD >may be the way to go as you can take lots of discs (which are fairly cheap) >and don't have to bother immediately offloading your recordings as you would >with some other types of digital recorders. > >Marantz PMD-670 ($600-$700). Uses CF cards. Sophisticated professional >recorder. Records in PCM, MP3 and MP2 at sample rates up to 48kHz. Supports >professional mics, selectable frequency band filtering, etc. Well designed, >easy to use. Very high quality audio. --