A magnetic recording/reproducing apparatus in which the reproduced audio data is processed and is recorded in every N cycles during which the reproducing magnetic heads scan a pair of recording tracks. The recording magnetic head is positioned behind the reproducing magnetic head for 8.5+4N track pitch, so that a write-after-read processing is provided. Using the recording head positioned behind the reproducing head, the reproduced audio data is stored in a memory for time base compression or expansion, and in a multichannel mode the reproduced audio data is read out and recorded performing write-after-read processing even if the number of channels is changed. The 2.sup.n channel audio data is recorded using interleave processing in every N cycles of the heads forming a pair of recording tracks so that even if the cycle in which a pair of recording tracks is not an integral multiple of the sampling cycle, the plural channels of audio data can be recorded and/or reproduced.