What about a dual mid-side encoder project?

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What about a dual mid-side encoder project?

Post by emrr » Thu Sep 16, 2021 11:57 am

Now that I’ve started taking dual mid-side mic rigs to live broadcast events, it has stood out that there do not seem to be any products addressing dual mid-side. Standard MS is problematic enough with digital consoles, most have no way to encode so at best you capture for future post, unless you add a set of preamps and an encoder. I don’t know how many would be interested, and it may be a tough crowd. I suppose the ultimate pie-in-the-sky flexible box would have:

Preamps and parallel unprocessed output path, bonus for interlock and cal for dual mid gain matching
Line input option (unity) and input splitting path
Front/rear mid pattern control
MS width control

This could be a useful tool for those in classical recording, film ambience capture, and live broadcast. It would apply to dual output mics used as mid. Ambisonic encoder boxes do exist, but I haven’t seen a DMS type.
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Re: What about a dual mid-side encoder project?

Post by mediatechnology » Thu Sep 16, 2021 4:25 pm

Sure!

I found this at Schoeps: https://schoeps.de/fileadmin/user_uploa ... 6-2010.pdf

Schoeps publishes the DMS-Splitter schematic that helped me wrap my head around how it's split prior to the dual MS decoders.

Image
Schoeps Double MS Breakout Box "DMS-Splitter"

I had actually thought about building an MS encoder/decoder into a stereo "Input-capacitorless" mic preamp for classical recording.
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Re: What about a dual mid-side encoder project?

Post by emrr » Thu Sep 16, 2021 6:42 pm

I forget about surround using mid front as center, and it’s interesting they do a split for that.
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Re: What about a dual mid-side encoder project?

Post by mediatechnology » Fri Sep 17, 2021 9:07 am

The other thing that becomes obvious to me from the break-out box is what is meant by "Double Mid Side" aka DMS.

Rear Side is a copy of Front Side.
Only the Mids are different.
It's "Double Mid (single) Side."

I think the reason that they split Center Off prior to decoding is due to gain weighting.
They mention that the coefficients of the encoder are adjusted for mic sensitivity.
Center derived as a copy of Front Mid may have different weighting.
B&H has the encoder for about $1300.
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Re: What about a dual mid-side encoder project?

Post by mediatechnology » Fri Sep 17, 2021 9:23 am

What about a dual mid-side encoder project?
Now that I think about it we already have one.
The encoder and decoders of the Mid Side Mini can be two decoders: One for Front and one for Rear.
I need to think about changing the encoder gain to make it match the decoder in that configuration but it would either be by jumper or THAT124X selection.
mediatechnology wrote:
Sun Aug 29, 2021 3:05 pm
This is the schematic for the "Mid Side MIni."

Image
Mid Side MIni Compact MS Encoder/Decoder
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Re: What about a dual mid-side encoder project?

Post by emrr » Fri Sep 17, 2021 10:32 am

That is a way to do it, and probably more in line with what many will want. I am working in stereo, so to me the main thing missing is the mid pattern control, and perhaps that's better as it's own module. Something to sweep between all available patterns, so gain manipulation per channel at line level, and polarity reverse on the rear to get the patterns towards figure 8. Essentially what the discontinued Sennheiser MKH 800 does onboard, and the MKH 800 Twin does not.
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Re: What about a dual mid-side encoder project?

Post by mediatechnology » Sat Sep 18, 2021 8:18 am

MKH 800 Manual: https://assets.sennheiser.com/global-do ... P48_EN.pdf

MKH 800 Spec: https://assets.sennheiser.com/global-do ... P48_EN.pdf

Image

Well there can't be too much going on in that small body in order to switch it internally.

On the Schoeps it looks like the pattern change switch only mutes the Center output.

The MKH800 looks to switch polarity and gain coefficients.

Any idea of which ones and how much?

It seems like gain/polarity on Mid Front, Mid Rear and Side would allow some wild changes in pattern.

Put three of these in the signal path:

viewtopic.php?f=12&t=812

As in IC4 here: viewtopic.php?f=6&t=681&start=10#p16482

I did a four speaker array for playback. viewtopic.php?f=6&t=742
Both Side and Mid were bipolar-firing.

As an experiment you should record RAW Mid F, Mid R and Side and then reproduce it using an MS speaker array.
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Re: What about a dual mid-side encoder project?

Post by emrr » Sat Sep 18, 2021 9:06 am

Pages 5 and 6 here detail the gain and polarity changes:

https://assets.sennheiser.com/global-do ... ual_EN.pdf
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Re: What about a dual mid-side encoder project?

Post by mediatechnology » Sat Sep 18, 2021 9:43 am

Image
MKH 800 Twin MS Patterns

Image
MKH 800 Twin MS Patterns

So you prefer a simple switch like the MKH800 over the variable MKH800 Twin?
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Re: What about a dual mid-side encoder project?

Post by emrr » Sat Sep 18, 2021 10:09 am

I have the variable MKH 800 Twin, and several other mics like it, but I can't use them for DMS in a live mix with most digital consoles.

A stepped switch that covers those patterns and those in between would inspire confidence and provide flexibility, though a fully variable tight tolerance pot would really be just fine in practice, I doubt anyone is sweating 'exact' textbook patterns, and they will change with the mic used, depending on front/back sensitivity differences. There's also side versus front/rear sensitivity to consider and adjust for, an example being MKH30 which is about 4dB less sensitive than the 800 Twin.

For example, if I'm doing a concert remote and have mixer space for a single stereo ambient element, an all-in-one would allow placement of a DMS array which I could set the pattern on while mixing, or even change between music and break periods. If it proved to be that the rear MS made for a better ambience in a mix than the front, then I could do it. I do all these things in post with raw F/R/S signals, but they don't make the broadcast mix. I'm sure there are others pondering similar solutions.

The thought of making separate front and rear MS as 4 delivered channels (or 5 for surround) is cleaner in some ways, but I frequently am fighting to retain free channels for ambience, with demands for additional stage sources always present.
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