Multiplex Filter vs ATRAC

Jacques Bouliane ([email protected])

This concerns the effect of any residual FM-stereo subcarrier on ATRAC compression.

I have a 2 speed 2-track Revox A-77 with which I can record the output of my FM tuner at 15 ips and play it back at 7.5 ips, bringing the 19 kHz stereo sub-carrier to 9.5 kHz, well within my hearing range. I was able to validate this a couple of times while recording from the radio, I do in fact hear the high-pitched 9.5 kHz signal. In this experiment I recorded from the radio with the JE-510, dubbed that over the Revox at 15 ips, and played it back at 7.5 ips.

Here are the results:

When there is no modulation (silence being transmitted) I can clearly hear the sub-carrier at half frequency. Any modulation will remove it however. For example with speech, it appears during the pauses, and disappears between them.

This would indicate that :

  1. The JE 510 responds to at least 19 kHz,
  2. ATRAC does its job of not coding the 19kHz tone when it would be masked by music and/or speech. No precious bits are lost on the coding of the sub-carrier, when the coder is busy with more meaningful content.

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