externally, there must be 2 cards installed in the computer, so that there is one physical output for each device.
COMPRESSION, DATA RATES, AND NETWORKS
The amount of data (the size) of a sound file is affected by several factors. The most obvious is the sample rate. A file recorded at
22.05KHz will take up half as much disk space as a file recorded at 44.1 KHz. Compression formats also greatly affect the file size. (This is not to be confused with dynamic range compression. This discussion pertains to data compression.) The formula for data rate, in bytes per second, is:
Rate=Fs x N x 2 /C
Where Fs is the sample rate in samples per second (or Hz), N is the number of channels, (2 for stereo, 1 for mono), and C is the compression factor. The “2” is in the formula because the sample taken is 16 bits, or 2 bytes. A stereo file, in PCM16, which is un- compressed, at 48 KHz, would use: 48,000 x 2 x 2 /1 = 192,000 bytes/second, or 11.5 megabytes/minute.
MPEG and ADPCM are examples of file formats which utilize data compression. MPEG is the highest quality compressed format available for this family of Antex cards. A file can be created which takes up one sixth or one eighth the space that an uncom- pressed (PCM16) file would take up, with sound quality that few people would be able to tell was any different from uncom- pressed. ADPCM was originally developed for voice applications, and does not sound as good as MPEG. There are several issues to consider when trying to decide whether to compress or not, and which format and sample rate to use.
MPEG has the best sound quality for the compression. Many different bitrates are available, to find the best compromise be- tween sound quality and disk space used. The disadvantages of MPEG are that it is not easy to edit a file after it has been re- corded. Antex offers a program called FastEdit, however, it is a very simple program which allows cutting the “heads and tails” of
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