August 2024 – Dr Badphil

Audio Gear

Sennheiser MZF 8000 ii

August 24, 2024

My series of field tests of the new Sennheiser MKH 8030 fig 8 (which kicked off with initial tests, moved on to mid-side recording, encompassed field recording, included comparison with the MKH 30, and most recently included use in a native B-format array) have led to various questions being asked of me, both via this blog and on sound forums. An interesting one was whether the mic needed the modular filter that Sennheiser make for the MKH 8000 series: the MZF 8000 ii. This filter was announced at the same time as the MKH 8030, in September 2023, but, as I understand it, was available beforehand as a special order option instead of the original MZF 8000. Both filter modules are the same in terms of the switchable -10 dB pad and the fixed low-cut filter of –3 dB @ 16 Hz (18 dB/oct), but differ with regard to the switchable low-cut filter: on the newer filter the latter is –3 dB @ 70 Hz (18 dB/oct), compared to the original’s –3 dB @ 160 Hz (which was much less steep too: I can find no authoritative specs). This stems from understandable user feedback, since a lower and steeper HPF around the 70 Hz frequency of the new filter is of more use to broadcast and filmmaking sound for those mics in the MKH 8000 series that don’t have in-built bass roll-off (i.e. all except the MKH 8060 and MKH 8070 shotgun mics): more use, that is, for reducing low-frequency wind noise and handling noise.

While some might (and, indeed, do) lament the absence of a built-in pad and switchable low-cut filter in the MKH 8000 mics, as found in the earlier MKH mics, the modular nature of the MZF 8000 ii filter means it is more flexible and, also, the end result is quite different. Flexibility is seen in the fact that the MKH 8000 mics, sans filter, can be kept small and, moreover, when the filter is used, this can be placed either between the head and the XLR module (making for a 29mm longer mic) or, if using an MZL cable, well away from the mic head, and next to the (then remote) XLR module. As for sonic differences between the MZF 8000 ii and the in-built equivalents of the MKH 30, 40 and 50, arguably the fixed 16 Hz low-cut filter of the former simply compensates for the increased bottom end of the MKH 8000 series mics, but there remains quite a difference in the switchable low-cut filters: the MKH 30, 40 and 50 have much higher and gentler low-cut filters, designed to address proximity effect, rather than the lower and steeper filtering of the MZF 8000 ii filter that is geared to reducing wind and handling noise. And, to add complexity, the MKH 20 switchable filtering is only concerned with high frequencies, being to modify the mic between near and diffuse field applications (with, of course, the proximity effect not applying to an omni anyway). The earlier MZF 8000 filter, therefore, was more comparable to the switchable elements of the MKH 30, 40 and 50, while the newer MZF 8000 ii is more overtly geared to production sound.

A pair of MKH 8030 mics: one with the MZF 8000 ii filter and one without.

OK, so much for the theory: how does the MZF 8000 ii perform? With the focus of the MZF 8000 ii on production sound, I fitted the filter to one MKH 8030 and mounted a pair of the mics in Rycote Invision 7 shockmounts to a short stereo bar on the end of a carbon-fibre boom pole. First off I compared the impact of mild shake (from straining muscles) on the two mics, with no high-pass filter (HPF) on the recorder, and just the fixed 16 Hz low-cut filter on the one with the MZF 8000 ii module fitted.

MKH 8030 on boom pole, with no filtering to remove low-frequencies arising from handling noise (note the scales and that gain was cranked up for all these tests).

Recorded simultaneously with the above, but recorded with a second MKH 8030 with the in-built fixed low-cut filter of –3 dB @ 16 Hz (18 dB/oct) of the MZF 8000 ii.

As expected, the MZF 8000 ii filter removes a significant amount of the infrasound, whilst having little impact on other low-frequency performance.

Moving on now to compare the effects of using the high-pass filters built-in to most recorders and mixers versus, or in conjunction with, that of the MZF 8000 ii filter, first of all I repeated the boom pole test with one mic with the recorder’s 40 Hz HPF (40 Hz being the lowest setting on Sound Devices 788T) with the other mic using the MZF 8000 ii’s 16Hz filter and the 788T’s 40 Hz HPF:

MKH 8030 on boom pole, with 40 Hz HPF on Sound Devices 788T to remove low-frequencies arising from handling noise.

Recorded simultaneously with the above, but recorded with a second MKH 8030 with the 16 Hz low-cut filter of the MZF 8000 ii plus a 40 Hz HPF on the Sound Devices 788T.

Again, as expected, the 16 Hz low-cut filter of the MZF 8000 ii adds significantly to reduction in handling noise from the boom pole by use of the recorder’s 40 Hz HPF.

For most such boom pole (or, indeed, pistol grip) mounting of a mic of course one would anticipate using a higher frequency HPF such as the switchable one built into the MZF 8000 ii, so that formed the next test: i.e. comparing the Sennheiser module with the 70 Hz HPF of the Sound Devices 788T.

MKH 8030 on boom pole, with 70 Hz HPF on Sound Devices 788T to remove low-frequencies arising from handling noise.

Recorded simultaneously with the above, but recorded with a second MKH 8030 with the 70 Hz HPF of the MZF 8000 ii.

Going by the frequency of the two HPFs some might expect that the results would be same, but the MZF 8000 ii’s 70 Hz filter has a much steeper slope (18 dB/oct) compared to that of the 788T (selectable at 6 dB/oct or 12 dB/oct: I used the latter), and this difference is clear. By contrast, the more recent Sound Devices 8-series and Mix-Pre recorders have 18 dB/oct HPFs, so the final test with the boom pole compared the MZF 8000 ii’s 70 Hz HPF to that of a MixPre-3: the latter only goes up in 20 Hz steps, so was set at 80 Hz.

MKH 8030 on boom pole, with 80 Hz HPF on Sound Devices MixPre-3 to remove low-frequencies arising from handling noise.

Given the steepness of the slope and the slightly higher frequency, the MixPre-3 shows more attenuation of boom pole handling noise.

So far, this is all very much as expected from the specifications: but where does this leave us? What are the benefits of the MZF 8000 ii in terms of its HPF if the recorder/mixer has one too? And, likewise, what is the benefit of the -10dB pad if, as is sometimes the case (e.g. the 788T), the recorder can supply 48v phantom power in line-input mode to cope with mics recording very high SPLs and consequently producing high outputs? Well, this is complex, and will reflect the type of material being recorded, the modus operandi of the sound recordist, and the capability of the mixer/recorder. In some cases, stacking HPFs (i.e. in both the mic and the recorder/mixer) may be useful to give a steeper slope: this is especially relevant if the recorder itself doesn’t offer anything as steep as 18 dB/oct. In many uses the fixed 16 Hz HPF of the MZF 8000 ii will be useful to remove unwanted infrasound, and many mixer/recorders do not have HPF options that go this low. In some cases the MZF 8000 ii will stop the mixer/recorder preamps being overwhelmed by, or giving too much headroom to, unwanted low frequencies: this is especially relevant with those recorders (such as the Zoom F8n) where the HPF comes after the trim/gain and ADC. Of course, any such uses need to be balanced against the additional weight of the module (relevant at the end of a long boom pole) and the lack of accessibility of switches if the mic is in a windshield. And it also needs to be considered against other options that are outside the mic or the recorder/mixer, such as the switchable 80 Hz HPF built into the XLR mount of the Rycote Nano Shield (and therefore accessible outside a windshield).

So, in short, it will come down to personal choices: the module is primarily of use to those for whom mic handling noise, wind noise, unwanted low-frequency ambient noise, and, for the pad, extreme SPLs are issues, which will mainly comprise production/ENG sound, sound effects recording, and, to a lesser extent, field recording. As for using the MZF 8000 ii with the MKH 8030? Well, although this has a decent bottom end for a fig 8 mic, it naturally has less in the way of a low-frequency response than its omni, wide cardioid, cardioid and supercardioid siblings and is also less likely to be swung around vigorously on a boom than, say, the supercardioid MKH 8050. In short, to date I haven’t found a need to use the MZF 8000 ii with the fig 8 MKH 8030: others may draw different conclusions. However, I’ve found it useful to have the MZF 8000 ii in the kit, and so far have used it most with just the 16 Hz low-cut filter with the MKH 8020, where the very bottom of the extended low end of this omni mic isn’t always wanted: and its good to be able to have the 70 Hz (18 dB/oct) filter and the -10dB pad there for whenever the need arises. Turning this around the other way, and again unlike some others, I’m glad that with the MKH 8000 series mics Sennheiser took a modular view to the HPF and pad capabilities since, for the bulk of my recording activities (and I suspect those of so many others), they aren’t needed and the consequently more compact form is useful: evidently the MZL cables take that compactness further, but that’s another matter!

And just for a size comparison here is my MKH 50 alongside MKH 8050 with the MZF 8000 ii. The latter adds to the size of the MKH 8050, increasing its length to 103mm and its weight to 81g: these are significant increases of 39% and 47% respectively from the MKH 8050 just with its MZX 8000 XLR module, but still well short of the MKH 50’s 153mm length, 102g weight and, of course, greater diameter (25mm vs 19mm).

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A tale of two MKH 8030 mics, a native B-format array and a pipe band. Part 2: recording.

August 4, 2024

Members of the City of Norwich Pipe Band arranged in two arcs, in the rather wonderful setting of Wymondham Abbey.

Introduction

In part 1 of the blog posts on recording test sessions with the City of Norwich Pipe Band (a prelude to a CD recording, with the tests focused on establishing whether recording indoors or outdoors is preferable), I covered the rationale and detail behind the microphone choices. To recap, with the band formed in both a circle and a near circle, I decided to go with a native B-format array of two fig 8s (Sennheiser MKH 8030) and an omni (Sennheiser MKH 8020), which, in terms of the required stereo end product, gave me options of mid-side with two fig 8s (i.e. decoding to a Blumlein pair), omni mid-side, and double mid-side (the latter with any polar pattern for the mid mics). And just to cover all bases, I also elected to add a spaced pair of omni mics (Rycote OM-08s). This second blog post is concerned with the recording and the results.

Location

Recording a pipe band indoors requires a large space. In the absence of a massive purpose-built recording studio (ruled out due to cost and because this was always intended as a location recording of a non-competition pipe band), I was glad to be able to arrange for use of Wymondham Abbey (many thanks especially are due to Brian Randall, churchwarden, for his help and support). The early 12th-century nave that survived the demolition of the rest of the abbey at the Dissolution (to function thereafter as the parish church for the town) is substantial, being twice the size of Abbey Road Studio One: if a small pipe band (the recording involved some members only – we had five pipes, one tenor drum, one side (or snare) drum and a bass drum) was to overwhelm the abbey church, then indoor recording would evidently be a non-starter outside a studio or concert hall.

Arranging the band

The regular formation used by pipe bands is a circle, and I could see no reason to, say, go for a more linear concert-style arrangement for recording. On the one side, recording a band in a circle is a challenge, but, as we have seen in the previous post on mic array selection, one that is solvable. But aside from the easy benefit of intervisibility for band members, this arrangement offers an additional benefit for loud acoustic instruments such as bagpipes and drums: direct sound will predominate over reflected sound from all directions. That is certainly the case if an unbroken circle is adopted, but balancing this with the array options (which included mid-side with two fig 8s) meant that these tests comprised both a full circle and a very broken circle – i.e. two opposing arcs each just under 90 degrees. With a modest contingent of the band for the test session, for the full-circle version we had the pipers occupying a little more than half the circle, which had a radius of around 2 metres. For the two opposing arcs, the pipers were all on one side facing the three drummers on the other side, with a radius of 3 metres for both arcs. We will replicate the arrangements for the outdoor test session in due course, but, evidently, any CD recording with a larger number of band members is likely to require some tweaking of the radius to accommodate everyone. That said, the band members were far from squashed together on this initial session.

Recording

Prior to the recording test session, I dropped into one the regular practices to meet the band. They hold these in the former Regal Cinema (now part of the Wymondham & District Ex-Services Social Club), so, while not a remote glen, it is far from a small room with a low ceiling. The sound of the band, however, came bouncing back from all directions and, given the reputation of bagpipes, I was a little concerned about levels before the test session. With only one pad on one of the mics (courtesy of the single MZF 8000ii filter I have – more on that soon) I was crossing fingers that I would be OK in terms of volume: with healthy max SPLs of 139dB for the MKH 8030s and 138dB for the MKH 8020, I was happy with the Sennheisers, but the Rycote OM-08 with its max of 127dB was an order lower. And then, what about levels into the recorder? Well at least with the Sound Devices 788T I had the option of using line inputs, which can still supply 48v phantom power, if things got overly hot. Needless to say, such slightly nagging concerns were entirely unfounded: with the more distant 3 metres of the two arcs I was able to set all the mic input trim/gains at 20dB, and with the shorter 2 metre radius of the full circle, I was fine with 15dB. Perhaps more reassuring too, the reflected sound in the aisled abbey church seemed much less overwhelming than the practice rooms: or was I just acclimatising!

Set up in the south aisle with the Sound Devices 788T. No overloading of mics or recorder, and I didn’t even resort to the earplugs I brought along!

The results

With the native B-format array, the options are endlessly variable, but what follows are some short clips (around 30 seconds long) from the beginning of Scotland The Brave (my request, as familiar to many: but we did record a couple of other tunes too), covering the main options.

Another view of the band set up in two opposing arcs.

Starting off, here are clips from the recordings of the band arranged in two opposing arcs:

First, we have fig 8 mid-side with the two MKH 8030 mics, which, of course, decodes to a Blumlein pair:

The stereo imaging is good for this, but the bass drum is very light. Looking at this in an FFT frequency spectrum analyser (Voxengo SPAN), the fundamental of the drum is around 35Hz, so the lack of low end in the MKH 8030 (whilst unusually good for a fig 8) is rather exposed. With a coincident omni in the array we can add this in a variety of ways, but just to keep things straightforward here is the same clip above with the bottom end of the omni MKH 8020 mixed in (with a 100Hz low-pass filter) at -6dB.

So now moving on to the omni mid-side pair itself, which, of course, has no problem with the bottom end of the bass drum. As you would expect, the drums have swapped sides (most obviously the snare is now on the left as it was in reality) as this and the subsequent clips don’t have the flipped LR stereo of the rear side of fig 8 MS and Blumlein pairs:

Leaving the various outputs of the native B-format array for the moment to compare omni-based recordings, here is the omni AB (spaced pair) of Rycote OM-08 mics at 840mm spacing (the spacing chosen to match the stereo recording angle of the Blumlein pair, decoded from the fig 8 mid-side pair, which lay behind the two opposing arcs formation):

Next up we have double mid-side. This uses forward and backward cardioid mid mics (created by mixing the omni and forward-facing fig 8 in the native B-format array) with the two resultant cardioid mid-side arrays mixed at the same level:

This might well be fine with the full band (and the low end is certainly present, due in no small part to the fact that the cardioids are created from a mix of the forward-facing fig 8 MKH 8030 and the MKH 8020 omni, so, as my preparatory tests demonstrated, have a better bass response than the MKH 8040 cardioid), but the level of the very small drum section is a bit low. Of course, we can change independently both the polar pattern of the two mid-side arrays that make up a double mid-side array and, more relevant here, can change the relative levels between the front and the rear. So here is more of the same, but with the rearward-facing component of the double mid-side array 6dB louder than the front:

And to demonstrate this flexibility a bit further, here is the double mid-side array again, but with the rearward-facing component of the double mid-side array 12dB louder than the front:

And then in a full circle, with a tighter radius.

Moving on, here are clips from the recordings of the band arranged in a full circle. Again the clips comprise the opening part of Scotland The Brave.

As before, first off we have fig 8 mid-side with the two MKH 8030 mics:

This still lacks the bottom end of the bass drum as with the fig 8 mid-side recording of the two arcs, but I must admit that the effect of the full circle (i.e. not avoiding direct sound from the side, with the consequent phasing issues arising from the fact that such sound is picked up by the front of one capsule and the rear of the other) is much less noticeable than I thought it would be. Perhaps that’s just my ears (I have been listening to a lot of bagpipe recordings over the last few days)! Anyway, I think it might still be one to steer away from and, accordingly, I haven’t included a version of this clip with added low end from a low-pass filtered omni mic.

On then to the omni mid-side pair, which, as before, has no problem with the bottom end of the bass drum. Again note that the drums have swapped sides (most obviously the single snare is now on the left as it was in reality) as this and the subsequent clips don’t have the flipped LR stereo of the rear side of fig 8 MS and Blumlein pairs:

Here is the omni AB (spaced pair) of Rycote OM-08 mics at 460mm spacing (i.e. narrowed from the previous 840mm spacing to give the wider stereo recording angle required for the full circle: 180 degrees):

As noted in the two opposing arcs set up, the drums in the double mid-side recording here are a bit on the quiet side, reflecting the lack of tenor and side/snare drums, although, perhaps counter intuitively, they are clearer than in the equivalent recording with the two arcs, despite the pipers spreading into the rear half of the full circle. As noted before, we can change, independently, both the polar pattern of the two mid-side arrays that make up a double mid-side array and, more relevant here, the relative levels between the front and the rear. So here is the same as before, but with the rearward-facing component of the double mid-side array 6dB louder than the front:

And to demonstrate this flexibility a bit further, here is the double mid-side array again, but with the rearward-facing component 12dB louder than the front:

High-frequency loss with vertical omni

As mentioned in part 1 of the blog post, omni mics are increasingly directional with high frequencies, which is the main reason to orient the mic vertically in the native B-format array if dealing with a sound source in a circle rather than, more typically, largely in front of the mics: that is, to ensure an even response in the horizontal plane round the full 360 degrees. But, of course, it also means that this approach reduces the high-frequency response (albeit equally) in the horizontal plane. As I said in the section on mic arrays, I didn’t expect that the high-frequency losses would be hugely significant with a pipe band: indeed, it could be useful given the nature of bagpipes and snare drums. I certainly don’t feel that results are weak in that regard, but, for the sake of completeness, here is a clip of the omni mid-side recording of the band in the full circle, with the omni mic given EQ to compensate as per Sennheiser’s polar plot for the MH 8020:

Processing

The native B-format array offers a lot of flexibility, which is only partly explored in the already rather numerous clips provided above. These have all been produced manually in Reaper, albeit using a mid-side plug in for the MS processing. Further tools can aid the process, be that Schoeps’s double mid-side plugin or, more usefully, plugins that can use the WXY tracks of the native B-format directly. So finally, here are the WXY clips (for both the opposing arc and the full circle set ups) for anyone who wants to play with them in an ambiosonic audio processor such as the Soundfield by Rode plugin, with which I have had fun dabbling.

The verdict?

Well this may be too early to call, given that this recording session was designed to be the first of two tests to compare indoors vs outdoors recording of the pipe band. The outdoor session will probably have to wait until September, due to holidays and a flurry of summertime engagements for the band, and then we will have to juggle the vagaries of the weather. But, even before this second test, I must confess I am much happier with recording the pipe band indoors than I was beforehand: I was very much in the ‘record a pipe band outside’ camp (indeed, perhaps the only voice in this case!). The set up in the abbey worked extremely well from my perspective: OK, the part-band was imbalanced in terms of pipes vs drums (and, indeed, imbalanced within the drum line with just one tenor and one side/snare), and there are some tweaks that I would like to make when we have a fuller drum line (e.g. bringing the tenor drums forward of the snare/side drums), but the acoustic was excellent and vastly different to the practice room.

And, beyond that, this first session has been extremely useful for assessing the different means of recording the band in a circle or in a broken circle of two arcs: I am happy with both formations although, of course, the different mic arrays performed differently in the two configurations of the band. The omni AB, or spaced pairs, worked reasonably, but lacked clarity on the snare drum so would require extremely careful placement of band members to get the (baked-in) balance right, if possible: in the context of a loud pipe band with members understandably not used to protracted setting up for recording and the lack of really good (and isolated) monitoring on location, I would be loathe to go down this route. This isn’t unexpected, as I included the spaced omnis as something of a control in this test. The native B-format array was a great success in giving so many options from a three mic set-up, and producing what I think is the better sound. Using the two fig 8 MKH 8030s alone, as a fig 8 mid-side pair, underplayed the low frequencies of the bass drum, understandably, but, as we have seen (or, rather, heard), this can be supplemented by a bit of bass from the omni MKH 8020 mic. Again using just two mics, the omni mid-side (MKH 8020 and MKH 8030) pair gave a good result in both the opposing arcs and full circle arrangements. The (virtual) double mid-side array from the three mics, however, is my preference: while sharing the ability to vary the levels of front and rear with a conventional double mid-side array (say made with two cardioids and a fig 8), the fact that in this case it was derived from the native B-format array gives it additional advantages. First, it keeps the low end intact (by virtue of the increased low-frequency response of the two virtual cardioids made by combining the MKH 8020 and forward-facing MKH 8030). And, second, it has complete flexibility in post in terms of the polar patterns of the mid mics. Playing around with all this is certainly easier in something such as the Soundfield by Rode or Harpex-X plugins, and they make steering the mic arrays (not that useful in this instance) easier too. In short, I’m really impressed by the MKH 8030 and MKH 8020 native B-format array for recording musicians in a circle: I suggest that it is worth giving something similar a go if you have a comparable challenge and suitable mics to hand.

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A tale of two MKH 8030 mics, a native B-format array and a pipe band. Part 1: the mic arrays.

August 4, 2024

Some of the members of the City of Norwich Pipe Band at Wymondham Abbey for the recording test.

Introduction

A happy coincidence of an interesting recording project and the arrival, a few weeks ago, of a second MKH 8030 fig 8 mic from the folks at Sennheiser set me thinking. The recording was to be of the City of Norwich Pipe Band: that is bagpipes and drums (side/snare, tenor and bass). Pipe bands often play in a circle, so they can all see each other, and for this recording the plan was to maintain that approach in broad terms. The circular formation, with the band members’ backs to any audience has given the BBC’s sound engineers a challenge when recording the world pipe band championships outdoors in Scotland each year. At that event they are obliged to record outside the circle formed by the band (who, to make things yet more complicated for recording, march forward while playing before forming the circle), making the best of a difficult situation. For this recording, which was not in the context of a competition or, indeed, a public performance, I had the advantages of a static pipe band, being able to place mics inside the circle, and, also, being able to tweak that circle idea a little bit.

Both the recording of a pipe band and the recording a group of musicians in a circle, or near circle, are challenges, and in this case extra complexity was introduced since the overarching aim was to do two test sessions, one inside and one outside, as a prelude to possible recording of a CD (opinions generally are a little split on whether a pipe band should be heard/recorded indoors or, in its more natural habitat, outdoors). Rather than one overly long write up, I am breaking this down into separate blog posts: this first one explores the mic arrays used, and the second discusses the recordings from the indoor test (and includes samples of them).

Options for recording musicians in a circle

There are various ways to tackle recordings of a circle of musicians, with the end results ranging from mono to surround sound: in this case we were after stereo. Obvious options for such recordings would be a Blumlein pair or mid-side with two fig 8s; omni mid-side; double mid-side; and a spaced pair of omni mics. The last three options would work with a full circle (though omni mid-side suggests flattening the circle a little front and back, due to less sensitivity of the back-to-back cardioid pattern of the resultant, decoded, LR stereo pair). And the Blumlein pair or mid-side with two fig 8s options suggest modifying the circle to form two opposing arcs, say of 70-90 degrees each, avoiding any direct sound from the musicians in the more difficult (i.e, phasey) side quadrants. Choosing from these options is not easy as there are pros and cons. Blumlein or mid-side with two fig 8s (which mathematically decodes to Blumlein, but which inevitably sounds a little different) offer the prospect of excellent stereo imaging, albeit with the reversal of the rear side (not an issue in this or, indeed, many situations); omni mid-side and spaced omnis offer the prospect of a better low end (relevant here to the bass drum); and double mid-side offers the scope of having different mid-mic polar patterns front and rear and, more significantly, the option of changing respective levels in post (useful for tweaking the balance of the drums and the pipes on either side of the circle). Well, given that this was to be a test recording, the obvious solution was to do all of these options simultaneously. This didn’t require a proliferation of mics vying to be in the same place at the same time, but, rather, a simple set up of three mics in a pantophonic (i.e. horizontal, or 2D) native B-format (WXY) array for all the coincident mic options, flanked by a pair of omni mics to cover the spaced-pair option. So five mics in total.

Spaced pair

The spaced pair of omnis option hardly needs much explanation, as it will be familiar to most, if not all, readers: the key points here being aiming the mics upwards to get an even sound in all horizontal directions (omni polar patterns being increasingly directional at higher frequencies), deciding on setting the height (with no musicians behind others and wanting to get a balance between upwards projecting drones at the rear of the pipers and downwards pointing chanters at their fronts, and to avoid over dominance of the snare drums (or, in the first test, single snare drum), I settled on 1500mm), and choosing a spacing. For the latter, with the full circle I wanted a stereo recording angle (SRA) of 180 degrees, so that meant a spacing of 510mm or less: I went for 460mm. For the two arcs, however, it made sense to narrow the SRA to match a Blumlein pair (i.e. 76 degrees) so that meant a spacing of 840mm. And for the mics, not having two more MKH 8020s, I settled on a pair of Rycote OM-08 mics.

Coincident arrays: Blumlein, mid-side, double mid-side, and native B-format

The native B-format set up is likely to be less than familiar to many readers. B-format components (W, X, Y and Z) can be derived from the A-format outputs of the tetrahedral (or, indeed, octahedral) arrangements of ambisonic mics, such as the Soundfield. With ambisonic mics, the W, X and Y components (we can dispense with the Z or height component here as irrelevant to our stereo end product) are derived from combining the different capsules, creating three virtual mics – forwards and sideways facing fig 8s (X and Y respectively) and an omni (W). A native B-format set up, needless to say, just uses two real fig 8 mics and a real omni mic. The combination of mics allows all of the planned coincident arrangements to be achieved and, indeed, allows the array to be steered: perhaps not that relevant in this case, though this could be handy for some circular set ups. The native-B array, which today can be found in single mics such as the Josephson C700s (for a cool £7,600), was pioneered by Dr John Halliday at Nimbus Records and is often referred to as the Nimbus-Halliday array: the two fig 8s (vertical and end-to-end) are separated by a forward-pointing omni mic. Such an arrangement wasn’t ideal for the purposes of this test: first off, in the Nimbus-Halliday array the omni is facing forwards, so the sound will be different from the rear; and, second, the mics aren’t as coincident as they could be (thinking here of comb filtering that will concern the purists) for some of the two-mic options first envisaged for this pipe band recording. For example, the two fig 8s, if used for mid-side, are separated by the omni mic, which would result in 54mm centre-to-centre spacing with two MKH 8030s: better than 68mm with a pair of MKH 30 fig 8s, but far from ideal. Taking suggestions by Daniel Courville and Paul Hodges of swapping the omni with one of the fig 8s (to remove the directionality of the omni mic at high frequencies) helps, but this can be much improved by rotating the whole array by ninety degrees, which swaps the orientation of the two fig 8s. This then gives a spacing of the omni and forward-facing fig 8 of 16mm centre-to-centre: very effective when combining these two mics to make a cardioid or, in different proportions, any other polar pattern for the mid mics in double mid-side. And the two fig 8s (thinking of mid-side with two fig 8s) become set at 27mm centres (half what they would be in the Nimbus-Halliday array if using the same mics); and, finally, the two most distant mics, the omni and side fig 8 (for omni mid-side) are at 43mm centres. Turning the omni vertical evidently reduces the high-frequency response in the horizontal plane a little, but, if required, a little high-frequency lift could be added. I didn’t anticipate this being much of an issue with bagpipes and snare drums: a little reduction in such frequencies could well prove useful. In terms of elevation of the array, this followed the height and rationale of the spaced pair.

Spot the difference! Left: the conventional, or Nimbus-Halliday, native B-format (or native 2D first-order ambisonic) array, which, top to bottom, comprises Y, W and X. Right: the revised version that I used, which, top to bottom, comprises Y, X and W. I used some thinner cables in the final version, not least as it made aligning easier when using shockmounts.

Taking the array outside: wind protection

With the pipe band test sessions being planned to determine whether any full recording session(s) for a CD should be recorded indoors or outdoors, the native B-format array needed to fit in a windshield. Inspired by ex-BBC sound recordist Roger Long’s experiment with a version of the Nimbus-Halliday array with the three mics (two MKH 30 and one MKH 20) all set vertically in a single suspension (the fig 8s side-by-side, and the omni in front), it is easy to rig the smaller MKH 8000 series mics in such a way as they fit into a normal blimp, which I duly tested (see photo below).

A very compact option for the native B-format array, fitting inside a standard windshield (in this case, a Rode blimp mk 1). I’d have been happy enough using it as shadowing effects and, indeed, any comb filtering arising from the non-coincidence on the horizontal plane are much exaggerated by the theoreticians that plague recording forums, but, given that I could fit the larger and nearer to ideal array into my DIY blimp, I decided against it for this project: but one to test more in the future perhaps as it is certainly much easier to manage in the field.

But given that use of the array in that set up means that the mics are not so well aligned in the horizontal plane, and that some will argue that acoustic shadowing results (always more theoretical than real), I thought it was just simpler and more consistent to use the same larger and more ideal array indoors and outdoors, taking advantage of my massive DIY blimp, originally built for LDC mics. A couple of welded additions by my ever-helpful friend Rob Moore, who built the original blimp basket, meant that the blimp was ready for my native B-format array.

And here’s the larger native B-format array inside my massive DIY blimp, originally built to accommodate an LDC mid-side pair for those occasions when extremely low self-noise is required: a few minor adaptations needed (thank goodness for its adaptable stainless steel construction).

Now by this point some readers may be wondering why I didn’t simply use an ambisonic mic. Well, other than not owning one and wanting to achieve a flexible approach with the excellent mics I am fortunate enough to own already, the key point is that the recording was not for surround purposes, but chiefly to determine the best approach for subsequent recording of a CD that is quite likely to involve a simpler approach. And, like many others, I have yet to be persuaded that the cheaper capsules in at least the more affordable ambisonic mics are in the same league as those of the MKH 8000 series mics. My biggest fear about the native B-format array was that the combination of mics – especially the combining of the omni and fig 8 – would fall well short of other MKH 8000 mics designed with a particular polar pattern. So at the planning stage I tested this by rigging an MKH 8020 omni and MKH 8030 fig 8 alongside an MKH 8040 cardioid, to compare virtual cardioid and actual cardioid mics. The consistency was remarkable, with the only audible difference to my ears being the slightly increased bass component of the virtual cardioid (not surprising: the MKH 8040 is no slouch in terms of bass, but it still lacks the bottom end of a pure pressure omni). So, happy with this key test, and with a workable native B-format rig, it was time to record: see part 2 of this blog post, for the first (i.e. indoor) recording session and results.

Top to bottom: MKH 8040 cardioid, MKH 8030 fig 8, and MKH 8020 omni. A simple test rig to compare the sound of the omni + fig 8 (mixed at 50:50 creating a cardioid) vs a purpose-built cardioid. This sort of virtual polar pattern creation is at the heart of the rig I was proposing, so thought a simple direct mono comparison like this a useful reality check before committing myself to recording with the native B-format array. The actual and virtual cardioids sound remarkably similar, although the additional bass response of the omni means that this is evident in the virtual cardioid: a high-pass filter could always reduce it if needed, but with the bass drum of the pipe band I thought this would be useful (as, indeed, proved the case). Changing the proportions of fig 8 and omni in the virtual mic means all polar patterns between fig 8 and omni can be created.

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