5.5 PC: BeOS BeOS is one of several other operating systems which run on the PC. It is optimised for digital media, so it's handling of sound and images is efficient. However, as with Linux only a small selection of hardware is supported at present. 5.6 What to look for in a soundcard There are some computer audio solutions which are better established than others, as discussed above. If an 'off the shelf' professional audio bundle is not an option, maybe due to cost constraints, then it is important to know what to look for in the technical specification of audio hardware. Here is an outline of the basics. Necessary connections: Line Input - for connection to the analogue playback device
Line Output - for connection to a monitoring system (headphones or loudspeakers)
These may be generically called analogue input and output.
Digital Input - only necessary if digital transfer is required. This will usually be of the S/PDIF type. In general, lower cost hardware will use mini-jack connectors for analogue input/output and RCA phono connectors for S/PDIF digital input/output (AES/EBU digital is usually via XLR connectors). On professional multi-channel cards, digital connections may be provided via TOSLINK, an optical interface. Some cards come with a break-out box, which may provide more robust connections. Look in detail at the technical specification of the ADC and DAC (the converters): look for signal-to-noise ratios (S/N) of at least 96dB (decibels), and a resolution of at least 16-bits. Some converters will offer higher resolutions of 20 or 24 bits. Check that the card is fully supported under your hardware platform and operating system: this is especially pertinent if using Linux, Be, or Windows NT. In general for lower end audio hardware, it is not sufficient to trust manufacturers' claims about compatibility. It is best to find and join appropriate mailing lists and newsgroups prior to purchase. Some professional level audio hardware may have multiple channels. This is superfluous unless you are digitising multitrack media. Some cards may not have analogue input/output at all, but may only support digital transfer - analogue input/output is essential if digitising direct from analogue sources. 5.7 Connections and additional equipment This section outlines the kind of connections that will need to be made between the playback equipment and the computer. Open-reel tape:
Line Output on the tape machine is usually via stereo phono or XLR connectors. These connect to the Line Input on the computer. There may be a playback volume control on the tape machine, which should be set using a test-tape and level meter (this may require specialist skills). Cassette:
Line Output (or playback output) is usually via stereo phono connectors. These connect to Line Input on the computer. The playback level is usually factory-preset. Records:
Turntable outputs are usually not at standard 'line' level, and cannot be directly connected to the computer; a suitable turntable pre-amplifier will be needed. Many domestic hi-fi amplifiers will do the job: connect the turntable to the Phono Input on the amplifier, then connect Line or Tape Output on the amplifier to Line Input on the computer. Select the phono input on the amplifier's front panel controls. Gramophone & phonograph:
These acoustic machines require a microphone setup, preferably in an acoustically dry and quiet space such as a recording studio. As previously stated, it is best to seek specialist advice before handling such media and playback equipment. Video:
VHS, S-VHS, U-matic, and Betacam video machines should have stereo Line Outputs for their audio signal. Some VHS machines may have 'Hi-Fi' audio output, which should be used if available. Some machines will provide audio signals via phono connectors, whilst others will have a multi-pin SCART socket. Other formats, such as D1, D2, D3, Hi8, Sony Digital Beta etc. carry digital audio tracks. It is important to use audio hardware which can support the correct type of digital audio signal. Film:
As mentioned previously, digitising film soundtracks will require detailed knowledge of the way audio tracks work for the particular format concerned. Different formats have used different numbers and types of audio tracks. Some have used stereo sound (e.g. Dolby Stereo), whilst others have used multiple channels for 'surround sound' cinema presentation (such as Dolby Six Track, Cinemascope, Dolby Digital). Some modern formats use digital audio (such as Dolby Digital and DTS), whilst older formats use analogue (such as Dolby Stereo and Cinemascope). It is best to seek specialist advice if digitisation direct from film soundtracks is necessary. 5.8 Storing the sound As each audio sample is digitised, it will need to be stored on the computer's hard-disk. Most software allows you to do this by selecting 'save' from a 'file' menu. Your sound will then be transferred from the computer's memory (which is cleared when you close down the programme, log out, or switch off the computer) onto the hard-disk (a magnetic medium that holds data when the computer is switched off or used for other tasks). When you want to access the sound again (maybe to play or edit it) it is read back into memory from disk. For very long sounds, there may not be enough computer memory to hold the entire sound; in that case, the sound is read in from the disk in chunks as it is needed. So when dealing with long sounds, it may be that the computer needs to access the disk often; for this reason, it is best to have a high-performance (i.e. fast access) hard-disk when dealing with samples of long duration. Hard-disk performance can be measured in access time for read and write operations, and is generally better for disks with higher speeds of rotation. It is worth paying for hard disk performance if there is lots of audio to process. Though storage of data on hard disk is generally reliable and fairly long term, it is not permanent and is still susceptible to mechanical and electrical failure. As a result, you should have way of backing up your audio files as you create them. You should also have a strategy for backing up and restoring all your data for the long term. Chapter 10 deals with these issues.
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