A serious mic collection...

Owing to a coincidence of circumstances, this is how my bench looks this evening...



:green:

keef

:shock: ... :shock:

:sad:
I've never had ONE on my bench ....

2 models there ? ... Keef, for those of us that don't see these things often, give us a run down of models and numbers and normal uses etc.

:thumb:

Soundfields?

:shock:

Some images come across a bit dark over here, forgive me.
Awesome.

Yep. Two ST250s, one MkIV.

The MkIV is being checked over prior to sale and a small problem with the 'elevation' circuit fixed (noisy Lm833).

The ST250s, one has a distortion on the headphone output (but the mic outs are clean) and the other ST250 has a PSU fault. -No +24V... Switch-Mode PSU and all surface mount... :evil:

The ST250s and the MkIV will all output B-Format, which allows you to "move" the mic after the fact by replaying the 4-channel recording through a decoder. The MkIV has a playback decoder built in, and this is the main difference between the two models capabilities.

There is a surround decoder for the 4-channel B-format signal, available as a plug in for Nuendo and Sadie V5... it will allow 8-channel surround or 7.1 or 6.1 or 5.1.... you can also get height/elevation outputs from it for "voice of god" signals (and "Voice of Satan" if you take the 'down' signals as well!!! :twisted: )

Keith

All fixed! :grin:

The dead supply ST250 had a shorted SMT chip capacitor adjacent to one of the SMT opamps on the top board... I'd looked at that mic before and decided to wait until I either got schematics or a similar mic to compare it to... In the end it took about an hour... I'm glad that I waited!!!

Happy Keef!

-Goodnight everyone!

Wow!

I wish I could put my hands on one of those at least for an hour to listen to...

What do you think about their sound?

I used a MkIV at Steve Albini's studio twice. Amazing stuff. I used it as a drum room mic. Who needs a reverb unit when you have one of these and a good room.

I need a reverb unit because I have neither. :sad:

Drool drool,

Their website rather cool. Just enough piccies and info to give you a hard on but nothing really given away, who can blame them.
There was a thread some time back (I think I may have started it) about the feasability of making something like this.
I think the capsule head is less of a problem than the encoder. There is a design somewhere on York Unerversitiy's website.
Although they were, I believe, intended as 5.1 mics I bet they get used more to give ambience. I have done this with an M-S mic placed at a distance from the sound source and it can give a "space" feeling. I guess a Soundfield would be way more versatile.
Steve

Soundfields default to an MS output since it's the easiest, most compatible output to default to. Mono fold-down is always trouble-free, since there's never any timing differences: the system is coincident as opposed to spaced.

If you could reasonably DIY a tetrahedral head assembly (which really is the hard part!) then all you nave to do is generate a B-format output of W, X, Y and Z. W is just all four added together, X Y and Z are different subtractions from W.

Once you have that, you don't need to build a decoder... make a digital 4-channel recording of the B-format signal and use the free software plug-in decoders, or alternatively try the .exe extractors, which will generate surround outputs... up to sixteen channels I believe... They are on the web in a few places, Geniuses like Dave Malham at York University (right in Zebra50's backyard!) have worked on this and done all the really hard digital work for you!

I wonder if Zebra50 would be interested in trying a tetrahedral array... if so, I wonder if Dave Malham would be interested in helping in a one-off joint DIY "project to end all projects"? :grin:

About the only other tricky thing would be the fact that the outputs need to be calibrated. The picture of the MkIV vontrol unit on the bench (the big blue one) shows that it had meters on it. In the old days of analog recording, where calibrations would drift and often be rather approximate, even an error of 1dB between channels ruins total cancellation when required... so the "back" of the cardioid pattern is nowhere near as "dipped" as it should be for example.

For that reason, the MkIV has an oscillator out, which not only provides level for calibration and polarity check to help avoid the "oops!" factor; there are "nicks" encoded into the tone, where it dims in level by about 20dB or so... it identifies the channels in case the tracksheet is lost... record at the head or the tail for calibration and/or channel ID. 'W' has no nicks in it, 'X' has nicks every second, 'Y' every 2 seconds and 'Z' every 4 seconds... easy and fairly instinctive to set up.

Now that digital recording means that calibration drifts of several dBs are in all reality a thing of the past, the ST250s just output a B-format audio signal, no test tones for setup. All you do is record it with the same gain on every channel. -For this I intend to build a 4-channel balanced-output ganged gain box for my own recordings. (I get to use the newer repaired ST250 any time I want in return for repairing it... how cool is that!!!)

If anyone really really wants to DIY a soundfield-type mic, it's definately a do-able proposition; I would think that the biggest hurdle would be calibration, assuming that we can accuratley make the tetrahedral array... -For me that would appear to be another obstacle, but I've seen enough here on the LAB that's made me marvel at what some folks like Stewart, CJ, xvlk, Jakob, Tim Campbell and the like get up to in terms of manufacturing, I really no longer doubt that it's possible.

A couple of notes from using them:

The array isn't as big as you think. The capsules aren't as big as you think. They look to be about 15mm each instead of 25mm. Also, they are arrayed so that if you stand "front and center" you're not looking straight into one. They are left and right at 45-degrees (plan view only) and each one tilts up and down at the prescribed geometric angle. This is important since moving around the mic in a circle, you never appear on-axis to any of the capsules, so there are no on-axis "hot-spots" where the axial HF rise 'brightens' the sound.

Remember, after recording, these mics can still be 'panned, tilted and Zoomed' in case the mic wasnlt pointed in the right direction or something equally bizarre!

How do they sound? -Well, very 'natural'. There's no "warmth", no "Smoothness", no "Harshness" no "Brittleness"... no nothing really. -That's not a bad thing for me, that's a perfect thing. Recording stuff like classical music, that's exactly what you want! If you think of mics that have a "sound" as being like colour filters that a photographer uses in front of the lens to "tint" the photograph, yes a progressive sepia graduation can make a beach sunrise look stunning... but it will ruin a saturday afternoon wedding party shot... same for mics... there is often no outright "good or bad" when you look at it that way... the safest way to make the recording is like taking a photo using clear glass... no coloration. After that you can build what you want with balance changes. That's how the Soundfield works. Would I use it as a vocal mic in a Rock tune? Almost certainly not. It doesn't make anyone sound like a rock star! -Other mics 'sort-of' help people sound like your favourite rock star... with these mics, Johnny Warshowski from down the street still sounds like Johnny Warshowski... not Axl Rose or whoever...

So it sounds real. Very real!

Cool.

Keith

Super post Keith,

I understand a lot better now, you make some interesting points.

The array,
This all depends on the capsules. I think they must be uni, condenser and have the most un-coloured response possible. That means small diameter polarised or back electret. Dave Malham used Panasonic capsules in his project and thats not such a bad idea to get something up and running. To make something like the real Soundfield is just jigging the angles which are all 60 or 120, it's like Origami. There is a post currently running about sounking capsules and they have small ones so that may be a source. To illustrate my point, take four coins or CD's of the same size and put them together as if they were the capsules. There is only one way that they all touch ( use plastacine to hold them together) it's just geometry. I have good workshop facilities ( lathes miller etc).

Calibration,
If I undestand you well this can be taken care of with the software plugin but you might need to further educate me there. If not I am sure we can think of something. I can see that the rear of capsule nulling, which is vital, can be set electronically.
This is do-able so lets do it. I f we could get Dave interested so much the better.
Steve

I wonder if Dave might be interested to know that we're having this discussion? I've never spoken or written to him, but I wonder if he'd find it interesting that we're contemplating this....

keith

Wow Keith... you gotta let me hear something you have done with those sometime. I'll host an audio sample if anyone's interested as well.

Re Dave,

I have been on his website sounds like a really nice guy. I guess the only way to know is to try him with the idea.
Steve

From the Soundfield literature:

the B-Format components are:
W = LF + RB + RF + LB
X = LF - RB + RF - LB
Y = LF - RB - RF + LB
Z = LF + RB - RF - LB
The 'B' Format signal can therefore represent sound from any point in space by 3 directional coordinates X, Y & Z, and the pressure component W.

Click to expand...

So if you calibrate each of the 4 microphone outputs in turn using a known acoustic source (pink noise, tone etc) either on a jig, before assembling them into the tetrahedral array, or by somehow arranging them to each recive the signal similarly after the array were assembled, then by building a 4-in/4-out matrix (needing only two dual op-amps) you should end up with B-format.

Keith

Yeah, it's not unlike GPS, but backwards if you follow me.
I would also like portable use, so I guess I would need a Decoder to give a stereo signal from the B format.
I have played a lot with the Panasonic capsules and in a normal way of thinking the are too bland and flat sounding but that might be just what is needed. They may not be very exotic but they would prove a point. They have significant rear pickup so the electronic nulling would be important.
Steve

The noise of the panasonic mic capsules might prove to be useless... certainly for classical use I'm just about certain it would. It would definately demonstrate the practicality though...

Yeah, it's not unlike GPS, but backwards if you follow me.

Click to expand...

Well.... what else would you expect, since it's an extension of the principles developed by Blumlein: the man who invented RADAR...



Keith

:green:
thanks Keef

I've nothing to add .. just happy to sit and read.
:shock:
shut up Kev ... just wanted to say... FANKS KEEF .. :thumb:

Yes, take your point about the self noise of the Panasonic capsules and as I want to use it as an ambience mic, noise is important.
Looking at Dave's design I now like the idea of a self contained unit that outputs B format and stereo which could be portable. I have never managed to master PCB design but if someone could do it ......
Has anyone e-mailed Dave yet? if not I could if it's deemed a good idea.
Steve

Wow, I learned so much about phase and how my ears relate to it the one week that we had a rental soundfield to record an 100 voice choir. Loved that rotate knob. I would have liked to get to take it apart and have a look at the insides. But I don't think that Dreamhire would have appreciated my attempts to 'tech' their mic.