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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
= 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).

Live Music

A European tour

January 8, 2021

An acoustic performance next to the Halle aux grains in Auvillar

With Brexit on its way, in 2017 I organized a small European tour for local band Rattlebox (for which I am sound-engineer). This was an exercise entirely determined by fun and entente cordiale: free gigs in some fairly random and mostly very small places in France, Andorra and Spain, largely determined – though not in all cases – by one of us having some connection; and six families, and a few extras, with us on what would be their summer holiday. Even so, there were practical issues to sort: arranging gigs (much helped by my French-speaking and living elder daughter), accommodation (largely campsites: this was a budget tour), power supplies, intermediary stops (this was part holiday, remember) and, of course, the PA. Anyway, here’s to the gigs:

Fri 28 July: Sainte-Sévère-sur-Indre (central France, midway between Bourges and Limoges). A fitting start to the tour: the gig was in the open-sided market hall in the square of the village made so famous by Jacques Tati’s 1949 film Jour de fête. We were a little nervous about the gig as we had no previous contact in the village, and had just had a few – hard won – emails with the mayor’s office. But they came up trumps, and had set out the market hall with benches (which filled up), put up posters, and even produced a few slabs of beer. We felt as welcome as the fair folk in Jour de fête. After a little electric shock (a reminder that wiring isn’t always what it should be), the technical side went OK: the PA was a combination of Alto and Proel speakers, with a Soundcraft mixing desk, all fairly basic but fine for what is a slightly raucous folk band. Beers after at a bar, then all of a hundred yards to the village campsite with its profusion of Swallowtail butterflies. Perfick, as Pop Larkin would have said.

Sat 29 July: Auvillar (Tarn-et-Garonne, south-west France). A weekend here in this most beautiful of small towns, courtesy of an old friend (a retired French general) and the indefatigable efforts of Gilles Compagnat. Unknown to us beforehand, Gilles organized everything, from a short taster acoustic session by the circular Halle aux grains (where our carefully transported English cider – yes, we took a present of booze to France – went like lightning), paella for all in the square, the main evening gig to an audience of 200 (then a record for Rattlebox) outside the church with its natural ampitheatre (with lights set up specially too), and a Sunday morning acoustic gig in the Place du Château. Having no PA to run on the Sunday morning, I set up a couple of omni mics and recorded the band outside, ambience and all. Goodness, were we sad to leave.

Tues 1 Aug: Vinça (Pyrénées-Orientales: southern France, near the east end of the Pyrénées). After stops at Carcassone, Lagrasse and, for some, the Med, this more workaday small town had a great lake and, by the side of this a lively bar  – the ginguette d’Aquagliss au lac. A compressed stage, but, who cares, there was more paella and dancing for the first time on the tour.

Thurs 3 Aug: Andorra la Vella. It had always been an ambition of Danny (of Rattlebox) to visit Andorra, and as we pitched up in a very urban campsite next to the national football stadium in insanely hot and humid conditions, we wondered why? But the evening gig in the Harlem Bar (organized by the remarkable Pierre Infante Lagrave and the bar owner Josu Adanez) was a great success: small, extremely sweaty and with enthusiastic dancing. What more can you ask for?

Sat 5 Aug: Junzano (near Huesca, Spain). Courtesy of  the sister of Simon (also of Rattlebox), a long-time resident, of this small village, we were part of the municipal fiesta, and welcomed enthusiastically yet again. A bigger stage and, for the first time, other acts: yet more paella (at least in Spain this time), dancing and, afterwards, sad farewells before the long journey home.

During all the mayhem of keeping things on track, running the PA, being the roadie, and occasionally snatching bits of holiday – all in the unremittingly fantastic weather – there wasn’t really any time for serious filmmaking, but here’s an extremely rough film (largely an aide-mémoire for us) that captures something of the fun and, indeed, the welcome: the eternal question down the pub is where next?

Film Projects Live Music

Busking in Andalucia

January 7, 2021

As live music goes, this was about as easy as it gets for the sound-engineer: the band (Rattlebox) decided on a long weekend in the south of Spain in May 2019, to play a largely acoustic gig at a bar and to busk for the first time. That meant no PA and no mixing, but I tagged along for the craic and took the chance to make a short film. Not as simple as you might think: the handy flight from Norwich to Malaga was delayed, and we only arrived in La Tahá in the Alpujarras in the early hours, and there was never a chance to catch-up on sleep. The band kept pace with the lack of sleep and the booze, but, goodness, I felt rough: getting too old for the rock ‘n’ roll lifestyle? And equipment-wise, things were tricky: it was nearly all hand luggage to keep costs low and to squeeze into the single seven-seater hire car, with underpants and socks stuffed into musical instruments, and my cabin baggage allocation mostly given over to the band. So I bought a Páramo Halkon traveller jacket with 15 pockets, which I stuffed with gear for that low-rent Hulk/shoplifter look. As for the gear, well that was mainly a Lumix GX80 camera with a Zhiyun Crane M gimbal, and a Sony M10 recorder with a stereo pair of Primo EM172-based Clippy mics): can’t get much more minimal than that.

It was a lively gig at the La Cueva de Mora Luna in Mecina Fondales on the Friday night, even if slightly surreal with cars driving past between the band and the audience. Spectacular pizzas afterwards on the house. The next night we were invited to a wake in the neighbouring hamlet of Ferreirola (never met the chap alive) and ended up muscling a grand piano down impossibly narrow streets followed by a local on her penny whistle. And on the Sunday we made it to Granada for busking. No time to visit the Alhambra, but made enough for dinner. Satisfying.

Anyway, here’s a rather rough and ready film that captures something of the weekend. The first song (Hares on the Mountain) was recorded back home in Norfolk, outside in the woods with a pair of Rode NT55s with the omni NT45-O capsules.