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November 2021

Audio Gear

A windy weekend with the Rycotes

November 8, 2021
Rycote HC-15 and HC-22 shotgun mics in Rycote Nano Shields: furry windjammers needed too in 34 mph wind.

Last weekend was blowy and autumnal here in Norfolk, so I had a bit of fun out in the wind with the Rycote shotgun mics that I have been testing, in this case with the new Rycote Nano Shield kits: the NS2-CA for the HC-15 short shotgun and the NS4-DB for the HC-22 medium shotgun. The Nano Shields are impressively light and small, even if the deliberately bendy (but resilient) structure seems a bit unfamiliar to start with.

First up, I simply stuck the mics in the garden of this quiet village, facing the road, so you can hear the sounds of wind in the trees, passing cars, and the odd actual shotgun going off. With no low-cut switches on either mic, the 80 Hz switchable low-cut filter on the XLR connector seemed useful so here is the HC-15 with no low-cut (or high-pass) filter:

And here is a recording made at the same time, but with the HC-22 and its low-cut filter switched on:

OK, there could be a difference between the two mics or the effect of the different sizes of their Nano Shields, so here’s the test reversed. First, the HC-15 with its low-cut filter switched on:

And then the HC-22 with no low-cut filter:

So the verdict: in high winds the Nano Shield 80Hz low-cut filter is effective, especially with mics such as Rycote’s own ones with no in-built filters. Evidently the new windshields and mics were considered together. There’s no sense that the wind is overloading the mic to the degree that the low-cut filter is too far down the chain to be effective. Of course, this means that you can apply a low-cut filter at the preamp stage: how good this is will depend on your preamp/recorder, but I found no discernible difference when using my Sound Devices MixPre-3 80Hz low-cut filter. This doesn’t mean that there is no value in having a low-cut filter at the Nano Shield stage since in severe wind conditions you can double up: e.g. set the MixPre-3 low-cut filter (perhaps to say 40Hz) and apply the Rycote 80Hz low-cut filter too.

While doing various tests in the garden, out of idle curiosity I also set the two shotgun mics up as a NOS pair (capsules at 30cm spacing, angled out to 90 degrees between the mics). Despite being manifestly different mics, the identical capsule and preamps mean that it works surprisingly well. If nothing else, it’s a demonstration of how well the two mics match if cutting from one to the other. Sorry about the rather theatrical footsteps stamping past at one point!

Out in the woods on a windy day with Rattlebox for some mic tests…

Off then to the woods to test the mics in wind on something different. Perhaps it’s just me, but the woods around north Norfolk in early November seem pretty dead in terms of sound apart from wind (maybe I simply lack the patience to lurk about for hours like a real wildlife sound recordist?), so for a bit of acoustic interest I persuaded Norfolk’s raucous folk band, Rattlebox, to do some unaccompanied singing (Dick Shannon’s ‘The Auld Triangle’): this was also for my tests on double mid-side recording with two forward-facing mics, for which see my separate post. Anyway, in terms of the Rycote mics, here’s a rather unfair test of the HC-15, pointing into a semicircle of singers – fine for the lead vocalist, but, as intended with a shotgun mic, rejecting much of the other singers in the choruses that were more side-on to the mic:

Combining with an AKG CK94 for a mid-side pair changes things rather, as you’d expect. The HC-15 works rather well in this manner:

Finally, returning to the stereo experiment in the garden (above), I set up the HC-15 and HC-22 as a NOS pair (as shown in the photo above – which also shows a double mid-side rig in a Rode blimp), with the following result:

Again, I’m not recommending mixing a short and a medium shotgun as a stereo pair, but it’s not bad.

So the final word on the wind tests? Well, needless to say these were much more extensive than shown in this short post, but it is clear that the Rycote mics handle themselves fine in windy conditions. The Nano Shields – which I haven’t reviewed as such – are a good match and their performance belies their small size and light weight. Finally, and rather incidentally, those slightly tongue-in-cheek NOS stereo pair tests with the two different mics confirm both that the off-axis sound is rather good, and that the two different mics match very well.

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Audio Gear

Variation on double mid-side recording

November 7, 2021
AKG Blueline mics used for these tests, top to bottom: CK93 (hypercardioid), CK94 (fig 8) and CK92 (omni): initial rig.
Second setup, bringing the three mics closer together (5mm apart): physically more stable, mics further from edge of the blimp, and fewer phasing issues.

Mid-side recording is a familiar technique to most sound recordists: a coincident stereo pair that is flexible and handy (not least as it can fit in a blimp or windjammer more easily than most pairs). I’ve written previous posts about my mid-side rigs, both for LDC mics and SDC mics. Double mid-side, where the fig 8 side mic is used by two mid mics – one facing forward and one facing backwards – is less used, but still well known, mainly by those recording surround sound. But, of course, the fig 8 side mic can also be shared with two (roughly) forward-facing mid mics: say one pointing up to the mouth of a singer-songwriter and one down to their guitar. Matrix the two mid-side pairs and you have stereo for both vocal and guitar, with reasonably little spill, and – with all three mics coincident – no phasing issues. Hugh Robjohns wrote an article for Sound On Sound about this use a few years back.

But there is another use for double mid-side with the two mid mics facing forward, and one that is rarely used or described: that’s where the two mid mics are pointing the same way but have different polar patterns. Using, say, omni and hypercardioid mid mics, you can matrix either with the side mic and get omni or hypercardioid mid side or matrix both and mix and you can get all the polar patterns in between for your mid mic: say, wide cardioid or cardioid as well as the omni and hypercardioid. This flexibility in polar pattern is quite separate from the familiar aspect of mid-side recordings, where you can vary the width of the stereo image by changing the proportion of mid to side mic: with this arrangement you get both stereo width and polar pattern flexibility in post, and – if using SDC mics – all with a very compact three-channel rig. As you can see, with a few Rycote back-to-back clips you can even fit it in a fairly standard 100mm diameter blimp.

Here’s a vocal test with a group (Norfolk’s raucous folk band, Rattlebox) arranged in a semi-circle around the mics outside on a very windy day (about 20 mph wind), singing Dick Shannon’s ‘The Auld Triangle’: the test was in part to see if the mics would be OK stacked in a standard (in this case Rode) blimp in reasonable wind (the top and bottom mics were nearer to the edge of the blimp than is ideal: at this stage I hadn’t come up with the more compact triangular array). The configuration needs the fig 8 centrally, which is good as fig 8 mics are the most sensitive to wind. The three mics had their 75Hz low-cut filters engaged to counter the wind noise. I matrixed, or decoded, each mid-side pair, so in the video you hear these on their own and then mixed 50:50. In the video, I call this mix of the two pairs a ‘virtual cardioid mid mic’) as it isn’t far off mid side with a cardioid mid mic: of course, a seamless range of possibilities from omni to hypercardioid is possible.

And here’s another test, this time with a guitarist (Luke Chapman) in his workshop (by day Luke is a woodcarver), with the same matrixing/decoding options. With no wind to contend with, the three mics have no low-cut filters engaged. Of course, the smaller sound source of a guitar means the changes in mid-mic polar pattern are fairly subtle.

How best then to process the three channels of audio in post? Well there might appear to be three options: 1) mix the two mid mics first, then decode to LR stereo as per normal mid-side; 2) decode each mid-side pair then mix the resultant LR stereo files; and 3) decode one mid-side pair then mix in the additional mid mic.

A bit of maths shows the first two are identical:

Mixing the mid mics first:
M = μM1 + λM2
L= μM1 + λM2+S
R= μM1 + λM2-S

Decoding each mid-side pair then mixing:
L1=M1+S L2=M2+S
R1=M1-S R2=M2-S
L=μL1+λL2
= μ(M1+S)+ λ(M2+S)
= μM1 + λM2+S

Decoding one mid-side pair then adding the M2 mic (centrally) to the stereo pair, however, gives a different result (as, indeed, you might conclude intuitively when thinking about it):
L = μ(M1+S)+ λM2
= μM1 + λM2+μS

So avoid this third option.

[NB I’ve just done the L channels in the second and third examples, to reduce the off-putting maths…]

In my case, I’ve gone for the second option as it is difficult to determine what mix of mid mics you might want – i.e. what mid-mic virtual polar pattern – without hearing the stereo sound. I must now set up my DAW (Reaper) so that raising one stereo channel reduces the other by the same amount to make assessing the balance/mix easier.

In terms of monitoring when recording you can either just listen to the channels in mono or, with any reasonable recorder, send two of the channels (the fig 8 and, say, the hypercardioid) to be decoded in the headphone monitoring or in the LR mix (either are possible on my Sound Devices MixPre-3): in this way you get confirmation that at least one of the stereo pairs sounds as you want it. With time on your hands, you can, of course, check the other pair in LR stereo too.

UPDATE (9.11.2021). By request I’ve recorded some ambiences (just my quiet Norfolk village street from my garden) with this rig and have uploaded the iso tracks (AKG CK92 omni; AKG CK93 hypercardioid; and AKG CK94 fig 8), the two separate MS recordings (as LR stereo) and the combined MMS recording (giving something akin to cardioid MS). These recordings were made with my modified array (i.e. the mics set in a more compact triangular arrangement, each only 5mm apart from the others).

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