m/s decoder

Posted: Thu Feb 15, 2007 12:54 pm

Two good points. Generally bi-directional mics do have smoother off-axis response. The question is does a given bi-directional mic have an over-all preferable sound than a given cardioid. The choice is completely dependent on situation and taste.

I agree with you that coincident mic technics (x-y, m/s) are most appropriate for small ensembles. However, there are a number of professional engineers out there who indeed employee m/s on orchestra's, opera and other large ensembles. The sonics are not my cup of tea, but the record sales obviously show that it can be successful.

Posted: Fri Feb 16, 2007 5:46 am

Boswell wrote:

Given the necessary limitations of the unit, I think the transformer M-S decoder for the headphone channel is a good solution, affording you the choice of L-R (in its various forms) or M-S miking in the field.

There may be a problem here that we have not considered because the Sowter, like other transformer decoders, is a passive device and therefore will incur an insertion loss of power. This could be a bad thing when driving it from the headphone output of the Korg, which is ultimately a low-voltage battery-powered device and can therefore only produce a relatively small output voltage swing (compared to a mains-powered device with supply rails of +/-15V or more). To get more power into the headphones requires drawing more output current, and that in turn requires lower impedance headphones.

This is particularly important in situations where it is necessary to monitor the recording while in the same space as the performers, because, with such a decoding circuit in place, it may be impossible to drive the headphones to a sufficient SPL for meaningful monitoring without clipping.

Although I was one of the supporters of the transformer solution, I was not thinking of the Korg's headphone driving capability at the time. I suspect an active device that decodes MS and drives headphones may be more appropriate. Or better yet, ditch the Korg and go with the SD!

Posted: Fri Feb 16, 2007 11:22 am

"The SD 744T has two built-in M-S decoders, one switchable to operate on channels 1 & 2 as a pair, and the other in the headphone output. So you can use a single M-S pair and two other mono mics and record 4 channels of decoded signals, using conventional headphone monitoring. OR, you can have two pairs of M-S mics and record them as M-S channels, using the headphone M-S decoder for monitoring. This may be what you want to do, but I'm not clear."

Boswell, thanks for taking the effort to answer my question.
I noticed that with the 744t, you can monitor an ms pair through
the headphone output without processing the signal. So what I
was wondering was if there were a cost effective way of monitering
2 ms pairs without processing (those 4 channels divided into two
separate pairs of ms). An expensive way to do it would be to use
2 Sound Devices recorders and combine the headphone outputs
to stereo. It's possible that there isn't a simple way of doing it due
of the nature of standard ms matrixes.

Reme, I am not impressed by your condescending attitude,
which has already been commented on in these forums.

Posted: Fri Feb 16, 2007 1:29 pm

aracu wrote:

"The SD 744T has two built-in M-S decoders, one switchable to operate on channels 1 & 2 as a pair, and the other in the headphone output. So you can use a single M-S pair and two other mono mics and record 4 channels of decoded signals, using conventional headphone monitoring. OR, you can have two pairs of M-S mics and record them as M-S channels, using the headphone M-S decoder for monitoring. This may be what you want to do, but I'm not clear."

Boswell, thanks for taking the effort to answer my question.
I noticed that with the 744t, you can monitor an ms pair through
the headphone output without processing the signal. So what I
was wondering was if there were a cost effective way of monitering
2 ms pairs without processing (those 4 channels divided into two
separate pairs of ms). An expensive way to do it would be to use
2 Sound Devices recorders and combine the headphone outputs
to stereo. It's possible that there isn't a simple way of doing it due
of the nature of standard ms matrixes.

I haven't got the 744T manual to hand, but my memory of how the headphone monitor works is that you have 20+ options to choose from, including having two M-S pairs as the four channels and alternating the monitoring between the two pairs. If you want to hear the summed L and R from the decoded M-S pairs, I think you're out of luck using the options available on the machine. However, if you were to select "Monitor 1+3, 2+4", you could get encoded M-S summed channels at the headphone jack, so an external transformer-based MS decoder would give you an L-R pair. Quite what that would mean as a sound field would depend entirely on your microphone placement, but presumably that would be your intention for post processing anyway.

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