There has been considered a digital tape recorder which records an audio PCM signal as parallel multitracks on a magnetic tape enclosed in a cassette casing by fixed heads. In case of recording and reproducing the audio PCM signal on and from the multitracks, there is a case where a fairly long burst error is generated in the reproduced signals from the adjacent few tracks which are included in a part of width of the magnetic tape. This phenomenon is caused due to scratches in the longitudinal direction of the magnetic tape or unstable contact between the magnetic tape and the magnetic heads due to the defective magnetic tape running system. When this burst error exceeds the correcting capability of the error correction codes which are used, the erroneous words are concealed.
As an error concealment, a method of interpolating by the mean value of the values of the correct words before and behind the erroneous word is used. However, if the correct words do not exist before and behind the erroneous word due to a long burst error, the mean value interpolation cannot be used. In such a case, the reproduced audio signal is subjected to preceding value holding or the muting.
As a digital tape recorder of such a multitrack type, there has been considered a recording method whereby the 16 -bit linear quantized two-channel audio PCM signal derived at a sampling rate of 44.1 kHz is recorded at about 1.4M bits/second on twenty tracks of the magnetic tape which is running at a tape speed of 4.76 cm/sec.
There has been considered another recording method whereby the 16-bit linear quantized two-channel audio PCM signal in the sampling rate of 48 kHz is recorded as the recording data of about 1.8M bits/second on twenty tracks of the magnetic tape which is running at a tape speed of 5.18 cm/sec (hereinafter, referred to as a 2M mode). Further, another method has been considered whereby the 12-bit non-linear quantized two-channel audio PCM signal derived by a lower sampling rate of, for example, 32 kHz is recorded on the magnetic tape at about 0.9M bits/second so as not to substantialy cause any trouble in the recording and reproduction in the audible frequency band (hereinafter, referred to as a 1M mode).
These recording methods are set in accordance with the particular end use or the like. In 1 recording method called the 1M mode, the amount of data which is recorded is one half as compared with that in another recording mode called the 2M mode, in which the number of tracks of recorded data is selected as 20, the tape speed can be reduced to half (2.6 cm/sec) of the 2M mode, thereby enabling a longer recording time to be obtained. On the contrary, if the tape speed is set to be equal to that in the 2M mode, the same amount of data can be recorded on the ten tracks. If the number of tracks is reduced to half, the track pitch can be doubled. Therefore, this makes it possible to easily manufacture multitrack heads and to easily perform the tracking operation upon reproduction. It is considered that this recording method using the 10-tracks in the 1M mode will come into wide use before the recording method using the 20-tracks. However, when superiority of the performance of the 20-tracks type is considered, there is a risk such that the 10-tracks type will have been neglected as an old-fashioned method.
Therefore, it is a requirement that the magnetic tape recorded by the 1M-mode method using ten tracks can be compatibly reproduced by the 2M-mode tape recorder using twenty tracks. This compatibility is needed to be satisfied as well even with respect to not only the track pattern but also the error correction codes.
Generally, in case of performing the error correction encoding process, if one symbol consists of a number of information bits, the encoding circuit becomes complicated and the time required for the encoding process becomes long. Therefore, one word (for example, 16 bits) is divided into the most significant eight bits and the least significant eight bits, and the error correction codes, e.g., Reed Solomon codes are constituted using these eight bits as one symbol.
In case of recording one word by dividing it into the symbols each consisting of eight bits in this way, it is necessary that both two symbols forming the same single word are the correct data upon reproduction. Even if one of these two symbols is the correct data, when the other symbol is the erroneous data, the correct one word cannot be obtained. Thus, it is generally required that the symbols forming the same word are included in a common series of error correction codes. However, in the case where the interleving process is also performed for improvement of the error correcting capability, the recording positions of these two symbols become a weak error correlation, such as being in separate tracks. Thus, there is practically a problem such that only one of the two symbols forming a word is found to have an error.
USPTO Backgrounds
USPTO Backgrounds