TABLE OF CONTENTS The application and value of the validity bit in each subframe were debated widely during the formulation of standards. Originally the V bit was designed to indicate whether the audio sample in that subframe was 'valid' or 'reliable', 'secure and error free' in other words, to show either whether it contained valid audio (rather than something else, or nothing), or if it was in error. It was set to '0' if the sample was reliable, and '1' if unreliable (so really it is an 'invalidity' flag). Since it is only a single bit, there is no opportunity for signalling the extent or severity of the error. What has never been clear is what devices should do in the case of an invalid sample and this is largely left up to the manufacturer. The most common use for the V bit is to signal errors that occurred in the transmitting device, such as when an uncorrectable error is encountered when replaying a recording, for example. But not all devices treat this in the same way, since some signal any offtape CRC error whether it was corrected or not, whereas others only set the V bit if the error was uncorrectable, resulting in interpolation or even muting in the convertors of most systems (this seems the more appropriate solution). But this is not the only use. Interactive CD (CD-I) players, for example, use the V bit to indicate that the audio data part of the subframe...
