Topic: Side mic from two Core Sound Cardioid Stealthy mics?

[morst]

It's been working for me for 30 years, no need to learn something far more difficult and complicated when I get better results than almost anyone who uses much more expensive equipment.

With that kind of talent what are you doing wasting your time on here?  Surely your skills must be in high demand.

Obviously I'm here to help the OP, who seems like a good guy, unlike some people around here.

your judgement is impeccable.

[robgronotte]

It's been working for me for 30 years, no need to learn something far more difficult and complicated when I get better results than almost anyone who uses much more expensive equipment.

With that kind of talent what are you doing wasting your time on here?  Surely your skills must be in high demand.

Obviously I'm here to help the OP, who seems like a good guy, unlike some people around here.

your judgement is impeccable.

Do you think a guy who entered the conversation just to make insults is likely a good one?

[grawk]

By telling him it’s bad to experiment?

[kuba e]

TheJez, it is a very nice experiment. For example, Octava does a similar thing. From the link you can see that it is not entirely critical to have a certain distance between the capsules.
https://www.oktava-shop.com/MK-012-100-Series-modular-system/Capsules/MK-012-figure-of-eight-adaptor.html?language=en

With the opposite connection of two cards to one output, I can think of only one small thing. I am not sure, it's possible that the impedance in the output of mics will increase. Also, double the current from the BB will probably be needed. But I hope there will be no obstacles in this.  Maybe someone who understands electricity might explain us.

What I read here on the forum and I hope I remember it well. The advantage of M/S is that the good fig 8 has an accurate unchanging polar pattern for most frequencies. We can get a more accurate stereo image compared to not top mics in XY. It's also a good combo for a shotgun. The shotguns are not suitable for good stereo image, but it can make a good mid signal for a main sound source. And the side signal can record the precise fig 8.

[heathen]

TheJez, it is a very nice experiment. For example, Octava does a similar thing. From the link you can see that it is not entirely critical to have a certain distance between the capsules.
https://www.oktava-shop.com/MK-012-100-Series-modular-system/Capsules/MK-012-figure-of-eight-adaptor.html?language=en

With the opposite connection of two cards to one output, I can think of only one small thing. I am not sure, it's possible that the impedance in the output of mics will increase. Also, double the current from the BB will probably be needed. But I hope there will be no obstacles in this.  Maybe someone who understands electricity might explain us.

What I read here on the forum and I hope I remember it well. The advantage of M/S is that the good fig 8 has an accurate unchanging polar pattern for most frequencies. We can get a more accurate stereo image compared to not top mics in XY. It's also a good combo for a shotgun. The shotguns are not suitable for good stereo image, but it can make a good mid signal for a main sound source. And the side signal can record the precise fig 8.

Another good thing about mid-side (though not necessarily exclusive to mid-side, to be clear) is that the mid mic will be directly on axis with the sound source and most mics have their best frequency response for the on-axis sounds.

[TheJez]

Thanks all for your support on this experiment. I've learned a lot already by just reading your replies. I've created a nice 'stand' to mount the two CSC's from a few childhood Lego parts, see attachment. Diaphraghm distance is about 4cm, just below 2". I hope that's ok for a faked side mic. These mics  are very unsensitive/quite noisy, so I need to figure out a good/loud enough setup for testing. I was thinking about passing trains or something.
First need to get an XLR connector and a mini-jack female connector to wire things up...
I was surprised to see how much emotions this thread evoked. Please be respectful to each other. This experiment is just for the fun of it.

[goodcooker]

Rigged up like this it's a similar distance as the AKG 522 XY stereo mic that I have. I've used it as a side mic in an impromptu mid side setup with a front facing cardioid a couple of times (you can adjust the included angle between the stereo capsules by turning a screw on the housing which moves the capsules inside mechanically from 90, 120, 150, 180 degree angles). It should work fairly well even though that much separation isn't ideal from a math standpoint.

Extra points for the Lego mount.

[Gutbucket]

Just came across this thread.  It can work, but..

There are a few ways to go about it, which I'll go into below. But regardless of how its done a fundamental issue will be how well the two cardioids used to produce the Side channel match each other in frequency response, level and phase.  The closer that match, or the closer those aspects can be made to match before summing them to produce the Side channel, the better everything else is going to work.  There are ways of getting that match close enough even if it isn't, but you will need to determine how far you want to go to achieve that.

The easiest and most flexible way of doing this will be to record the three mics to three separate channels, then produce the Side channel afterward on the computer.  Not only will that not require any custom wiring or connectors, but it will allow you to improve the match between the two cardioids if required.  If the two cardioid signals match perfectly (unlikely), all you'll need to do is invert polarity on the right-facing one and sum them together to produce the Side channel. If they don't, you be able to compensate for the mis-match to some extent, determine the extent of the mismatch, and determine how well this is capable of working, to determine if its worth pursuing.

^
That method of recording all three mics separately requires a multichannel recorder to produce a stereo mid/side recording.  Would be a good application of the three channels of a Mixpre3. But even if you don't have a multichannel recorder available, you can use a two channel recorder to do initial testing to determine how feasible it will be in practice and if it makes sense to pursue further.  In the best case you may be able to use a two channel recorder (more on how you can do that in a following post)..

First, best to do an initial check of the match of the two cardioids and their sum to fig-8, which you do using a two channel recorder.  Couple ways to do that..  try both!

Method A (simpler, more clear immediate result)
1) Place the two cardioids as close together as possible, pointing the same direction.  I'd actually tape them together, just don't cover the side vents.  Record each microphone to a separate channel as usual - you can use a two channel recorder for this if a multichannel recorder is not available.  Produce a steady tone or noise on your phone and place that directly in front of the recording rig. Record some of that noise using identical gain for each of the two channels.

2) Transfer the recording to the computer.  Flip polarity on one channel (normally the right one, but doesn't matter in this case).  Sum the two to mono.  Place the faders for both channels at 0db gain and listen to the noise.  Slowly move one of the two faders.. move it up, move it down..  Search for the point where you achieve maximum cancellation of the noise that was being produced by the phone.  You wont achieve total cancellation, but you do want to fine the point where the cancellation is strongest and the noise is quietest.  Once you find that, note the difference in gain between the two faders. If the mics are perfectly matched, both faders will have the same position.  If they aren't you'll know know which is more sensitive than the other, and by how much.  At that point if you mute either channel the noise should increase significantly, but with both unmuted, the noise should be as quiet as possible.  Once that's done, you'll always apply that difference in gain between the two cardioid channels which will get summed to produce the mono Side signal. More on additional ways of improving the match in a later post..

Method B (closer to the required end result)
1) Take your 180 degree angled cardioid rig outside away from reflective surfaces so as to emulate an anechoic space as much as possible.  Record each mic to a separate channel as usual - you can use a two channel recorder for this if a multichannel recorder is not available.  Produce a steady tone or noise on your phone and place that directly in front of the recording rig, 90 degrees off axis from both of the cardioids, and centered between them. Record some of that noise using identical gain for each of the two channels.

2) Same as before.  The cancellation you are able to achieve will be significantly less, but go through the process again and see how good you can get it.  Difference in gain should be the same as in method A.

Okay, let's assume the match between the two cardioids is good and you are able to achieve good cancellation using the same level of both channels with no other adjustments.  That's great. It means it may work practicality without too much post work, and means you may even be able to use a two channel recorder with balanced inputs along with some creative wiring in place of a multichannel recorder.

Regardless if you end up using this for actual recording and the particulars of how you end up go about doing it, the ability to achieve a decent fig-8 null is going to be a key indicator of probable success and can be loosely confirmed via these tests.  You can do them without any additional equipment, and if they work out, things are promising moving ahead..

[Gutbucket]

Backing up to try and clarify a few comments about stereo - through the PA, in the room, via mic configs and our recordings.

The sound of any live performance, as heard in the space in which it was performed, is always multi-dimensional.  Even if reinforced from a single speaker PA, even if there is no PA and only a single singer standing alone on stage, the sound as heard in the performance space is multi-dimensional.  We can choose to capture that multi-dimensional complexity with varying degrees of dimensional "freedom" by way of additional recording channels.

2-channels can be used to very usefully capture and reproduce part of that multidimensionality. "Stereo" is a somewhat loaded word, used to mean different things.  The type of "stereo" that a two channel of PA provides is generally not the same as the type of "stereo" that reproduction over two speakers or head-phones provide.  Usually there is much less "close your eyes and you can still point at the particular instrument" type of imaging through a "stereo PA", because that type of stereo would only work for audience members sitting in the center.  But other stereo aspects which convey a different kind of dimensionality can be used that work across a widely-distributed audience. Certain sounds can be dynamically panned around with movement heard from everywhere, sources can be "spatially enhanced" with chorus, delay, or what have you.  Mostly conveying "stereo effects" rather than static image positions.  Yeah, there may be a little static panning, say of drums, but not much.

If we record using only a single channel we flatten that complexity down to mono.  Take the example of a single close mic'd SBD channel.  Lets say a single vocal mic.   The mic is placed close to the singer to pickup only the direct vocal as much as possible.  Anything other than the vocal which also gets picked up is also there in that channel, but will be flattened to mono, "mixed in" along with the vocal.  To reduce that as much as possible a directional microphone is placed very close to the singer which helps minimize the pickup of everything else, which is about as isolated as that single channel of vocal can practically get.

If you record that SBD feed you pretty much get just that vocal.  But if you record using a single microphone from a position farther away, say out in the audience, even a very directional microphone pointed directly at the singer is going to pickup not just the sound emitted directly from the singer themself but also the multi-dimensional sound of the singer's voice exciting the acoustics of the room.   If there are any other sources of sound in addition, onstage, audience members, whatever, they get included as well.. and it all gets flattened to mono.  We cant totally eliminate pickup of the sound of the audience members and the sound of the vocal bouncing around the room.   We can only arrange things to maximize pickup of the direct-sound coming from the singer, and minimize the pickup of everything else as much as possible.

Ok so instead of one microphone say we use two and point them both directly at the singer. Since both are pointed directly at the singer there is not any additional "audience and room sound" than there was before when using a single microphone.  Our primary goal is maximization of the singer over everything else, so we don't want to point the second microphone elsewhere.  Instead we keep both pointed at the singer and introduce use some space between the two microphones.  We now captures an additionally aspect of dimensionality.  The room and audience stuff pretty much remains at the same level as before* but isn't mashed in with the vocal as much.  It's instead spread out more.  This type of stereo is somewhat more akin to "PA stereo" than typical home playback stereo.  When we want as much clarity and focus on the primary source as possible it makes for a quite reasonable approach.  Increasing the spacing between a stereo pair of mics setup with very little, even no angle between them to achieve reasonably good sounding stereo playback is the essence of the Improved Point At Stacks microphone technique, and leans on stereo aspects other than  static level differences between channels, somewhat similar to how stereo PA mixing works.

[TheJez]

Just came across this thread.  It can work, but..

Method A (simpler, more clear immediate result)
1) Place the two cardioids as close together as possible, pointing the same direction.  I'd actually tape them together, just don't cover the side vents.  Record each microphone to a separate channel as usual - you can use a two channel recorder for this if a multichannel recorder is not available.  Produce a steady tone or noise on your phone and place that directly in front of the recording rig. Record some of that noise using identical gain for each of the two channels.

2) Transfer the recording to the computer.  Flip polarity on one channel (normally the right one, but doesn't matter in this case).  Sum the two to mono.  Place the faders for both channels at 0db gain and listen to the noise.  Slowly move one of the two faders.. move it up, move it down..  Search for the point where you achieve maximum cancellation of the noise that was being produced by the phone.  You wont achieve total cancellation, but you do want to fine the point where the cancellation is strongest and the noise is quietest.  Once you find that, note the difference in gain between the two faders. If the mics are perfectly matched, both faders will have the same position.  If they aren't you'll know know which is more sensitive than the other, and by how much.  At that point if you mute either channel the noise should increase significantly, but with both unmuted, the noise should be as quiet as possible.  Once that's done, you'll always apply that difference in gain between the two cardioid channels which will get summed to produce the mono Side signal. More on additional ways of improving the match in a later post..

ss if you end up using this for actual recording and the particulars of how you end up go about doing it, the ability to achieve a decent fig-8 null is going to be a key indicator of probable success and can be loosely confirmed via these tests.  You can do them without any additional equipment, and if they work out, things are promising moving ahead..

Thanks Gutbucket for pointing out this important key to success, and for proving such clear instructions.
As I don't have a multitrack recorder, my only feasible way to go is to electrically sum the channels to turn it into a mono channel, then connecting the mid microphone as 'the other channel'. I do realize that the CSS's would have to match well to get acceptable results with this setup, so I gave your Method A a go...
I've created two test tracks: One with a 1kHz beep (1 second beep, one second silence, repeat), one with white noise, and played these through my stereo set. I've put the two CSS's together with a tiny elastic band. (The CSS's are so tiny that it is almost impossible to tape them together without covering the vent holes). I put them close (about 7") to the speaker and played & recorded the test tracks at the highest volume allowed without getting complaint from the neighbors (to minimize influence from ambient noise).
When doing the trick described in step 2 (after normalizing the recordings), after applying a -0.3dB attenuation to one of the channels:
- I got the beeps down from ~-3dB to ~-18dB VU level
- I got the white noise down from ~-3dB to ~-12dB VU level
This is the best volume reduction I could achieve, which would mean the CSS's sensitivity would about 0.3dB apart.This doesn't sound too bad for using the electrical sum of the two, right? I don't have much choice anyway  . Or would you think this difference in sensitivity is already disastrous when doing electrical summing?

While processing the results of the test track recordings I did notice once again how incredibly noisy these mics are. (Especially since I now can compare with the SP-CMC-4's and the Clippy's I recently got.) I've made so many great loud concert recordings with them over the past decades, but result with lower volume recordings is simply not good.

[Gutbucket]

Getting somewhere!

Okay, let's make a few assumptions:  Let's assume the only difference between the two mics is that slight difference in sensitivity, frequency response and phase response are identical, and we somehow achieve perfect geometry. In that case, flipping polarity of one channel and summing the two will produce a slightly lopsided fig-8 pattern.  The null plane will skew toward the less sensitive mic side somewhat.  You essentially create a pattern somewhere between fig-8 and hypercardioid, pointing in the direction of the more sensitive mic.

If you were to further increase the level difference between channels, say by incrementally reducing the gain of the less sensitive mic, the null plane will continue to shift further toward the less sensitive side and become more cone-like as the pattern morphs through supercardioid and eventually to cardioid once the less sensitive mic contributes nothing.

How asymmetric is the resulting fig-8 pattern? You might try putting the two mics together facing opposite directions as described in method B and set things up so as to be able to monitor through closed headphones while recording or in rec/pause.  Listen while moving a constant noise source around the the mics (as mentioned above, it will probably help to do this outside where there are few reflections and little room reverberation).  Doesn't have to be very loud, but the headphones or in-ears need to isolate well.  While moving the noise source around the mics listen for the drop off in sensitivity which defines the null-plane.  In that way you'll be able to determine how far off-center it lies.

The more off center it is, the farther the stereo image will be panned over toward the more sensitive side when using the sum as Side channel in a Mid/Side recording.  If its close enough to center the difference in sensitivity may not matter much.

[Gutbucket]

I don't have much choice anyway 

Actually you do.. or might, depending on the gear you have at hand.  Even if the plan is to differentially sum the to mic signals to a single channel at the balanced input to the recorder, there is still a way you can adjust levels prior to that summing so as to produce a more symmetric fig-8 pattern.

You just need to use preamp that features separate gain adjustments for each channel.  You can then match levels by carefully tweaking the separate gains, and lock them down so they can't be changed.   I've done it myself using a CA-UGLY (which features independent channel gain adjustment trimmer pots). In that case I was recording two back-to-back cardioids to two channels of a DR2d.  Recording both channels would have allowed  for adjustment of levels afterward if needed, but I was using the CA-UGLY to power the two cardioids anyway, so it made sense to get the levels matched prior to the signal reaching the recorder.  More details on that if interested. It works but may be fiddly dialing it in as perfectly as possible.

After getting the pattern as symmetrical as possible using the channel gains of the preamp, you'd then switch over from inputting both channels to the recorder to summing them into a single differential balanced input channel instead, freeing the other recorder input for the Mid microphone.  Just need to make sure the preamp gains are fully locked down afterward so they don't get changed after that.

To differentially sum into a single balanced recording channel, connect the signal output ground/common from the preamp to pin 1 of the balanced input on the recorder, the left-facing mic + signal to pin 2 and right-facing mic + signal to pin 3.   You'll then be recording a symmetrical "fig-8-ish" pattern to a single channel of the recorder.

[Gutbucket]

Another important detail is the geometry of this thing.  More on that later.

[grawk]

if you look at this as an exercise in understanding what is going on with mid-side processing., it's a great idea.  If you look at this as a way to make pleasing recordings, it's a lot of pain for a worse result.

[Gutbucket]

^ Probably.  Fun to discuss and mess around with at least..  and might actually work well enough to prove useful. 

I got close to this in figuring out a way to run a Naiant X8 fig-8 as the Side mic in a four channel stealth setup into an unbalanced recorder years ago.  I did have the advantage of the Naiant X8, which consists of two back-to-back unbalanced electret cardioids in a single housing, already having its geometry and channel matching worked out.  While the X8 is primarily intended as a low cost balanced output fig-8, it can also serve as two separate unbalanced back-to-back cardioids.  So I powered the individual capsules separately using the two channels of the CA-UGLY and recorded the unbalanced outputs into separate channels of a DR2d for initial tests.  That worked.  The next step would have been differentially summing the outputs of the preamp to record the Side channel to a single unbalanced channel.  That should have worked fine, but didn't take it farther for other reasons.

Intention was turning the center chest-mounted omni of my 4 channel LRCB torso baffled stealth setup into a Mid/Side stereo pair.  The X8 was hung around my neck upside-down, resting just above the center chest-mounted omni.  Problem was not so much the unbalanced Side channel scheme but not having sufficient channels to do what I really wanted.  Being restricted to four unbalanced channels with the DR2d, I didn't want to give up the existing rear facing omni channel, and running both would have required two DR2d along with syncing in post.  Too much hassle.  If I'd had six channels available in a pocketable recorder I would have gone forward with it and eventually rigged it up so that the rear-facing omni formed a second Mid/Side pair using the other X8 I have on hand, along with trying a few alternate configurations.