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Mid-side with AKG CK94

May 25, 2021
AKG CK94 (top) and CK93 (bottom) in Rode Mk1 blimp suspension

I’ve had one of the AKG Blueline mics for years. This has the CK93 capsule, which is an excellent mid-price hypercardioid SDC mic that has proved great for booming indoor (and, on occasion, outdoor) dialogue. I have also used it for music recording where I needed a narrower polar pattern than cardioid. It is leagues above my Oktava MK012 hypercardioid – so beloved by indie filmmakers – in terms of build quality, handling noise, and features (having low-cut and attenuation switches).

From time to time I’ve wondered about the other interchangeable capsules in the Blueline range and, above all, about the CK94 – the figure of eight capsule. Of course LDC multi-pattern mics include a fig 8 polar pattern and, paired with another mic, this allows mid-side recording, which I have done many a time. And, as I have posted, with a massive DIY blimp I have even got such an LDC pair outside for field recording. That said, it would be useful and, for most uses, more practical to have a compact SDC mid-side pair. The standard for field-recording pros is the Sennheiser MKH30, which, while excellent and with the advantage of humidity-beating RF technology, has the distinct disadvantage of cost: it has a street price of around £1500, and even used ones seem rare below £1000. Add another Sennheiser MKH mic (say an MKH40) and wind protection to fit and you will need to spend £3000 or more. Unlike other polar patterns, SDC fig 8s are rare, and there are few more affordable ones: ignoring the clunky pseudo fig 8s made by Oktava and Kortwich (made using two cardioids mounted back-to-back, giving a T-shaped mic), the only affordable true single -diaphragm fig 8 other than the AKG CK94 is the Ambient ATE208 Emesser. The latter, however, has a lot of bass roll-off due to it being tailored to match the off-axis response of a shotgun mic (its intended partner). Recently, boutique Taiwanese mic-maker B9Audio has produced the CM180, but it is only available direct from the maker: so this means significant shipping and duty costs need to be added to the US$749 price. Reviews are also thin on the ground to say the least.

So, with all this in mind, the AKG CK94 remains the most viable affordable SDC fig 8 for general usage (i.e. music as well as film sound). Although now out of production (AKG/Harman/Samsung appear to be phasing out the whole Blueline family and the CK94 was the first to be discontinued), at the time of writing it is just possible to find one or two new examples for sale: with the SE 300B amplifier/mic body, street price is around £600. But I’ve been keeping my eye on the used market, and was please to spot one on the Saturn Sound website (where there is a list for a grand closing down sale of mics – with some very rare examples), and – together with the SE300B amplifier/mic body – the other day I became the owner of a very good condition example: indeed, during a pre-sales check, Ashley Styles of Saturn Sound thought the capsule a bit noisy and replaced it with one he still had. All this, plus delivery in person (he has retired not so far away), for a remarkably affordable £200.

I had no concerns about the CK94 for music or louder effects recording, but, with 22dBA self-noise (a long way from the MKH30’s 13dBA) my hopes were low for recording quieter ambiences. So I was surprised how good it sounded during an initial test recording the ambient noise in the garden (in a village in rural Norfolk). You can have listen here:

I was expecting something much noisier.

In terms of rigging it up for field recording, I purchased a couple of the older style (i.e. lower profile) back-to-back clips made by Rycote (ref. no. 048460), which, unlike the new fit-any-mic clips Rycote make for MS pairs, neatly fit into a Rode Mk1 blimp and have lugs to attach to the suspension bands: the mics sit centrally and with a healthy blimp diameter of 100mm there is still plenty of air space around both mics. The CK94 has to project further forward given the location of its capsule (the centres of the two capsules should align, of course). I’ve added a DIY conn box equivalent (a clamp for the two thin cables – Sommer Cicada – that go from the mics to the DIY boompole-top XLR holder) to avoid the two heavier cables entering the blimp, so I’m there with a very nice sounding SDC mid-side rig for a very modest outlay. And, of course, I can use the AKG C94 with mid-mics other than the hypercardioid CK93: for example, my Rode NT55 mics give me cardioid and omni mid-mic options. I’ll post other recordings – including music – with the CK94-based mid-side rig in due course.

With blimp on, and showing the double XLR holder at the top of the boompole
And a close-up of the DIY double XLR holder at the top of the boompole
Audio Gear

Testing the new Rode Wireless GO II

February 27, 2021
Rode Wireless GO II recording into an Android phone

Putting your equipment through its paces is part of getting to understand it properly. Given its newness (only released this week), my tests on the Rode Wireless GO II might be of wider interest: so here’s a post about them.

First, a quick bit of background. I’m not normally in a rush to adopt new technology, but this week – following the death of an old handheld recorder (my Sony M10) and while planning a couple of projects – I was looking at lav mic self-recording back-up options, and Rode’s new offering seemed on the nail and very timely. I know the first version was nothing like a professional wireless mic set up (not least for its dropouts when out of line-of-sight), but I’d found it eminently usable for the particular and less exacting uses I bought it for: in particular, the sound quality stood up compared to the same lav mic hard-wired. So, rather than wait for anyone to get round to a thorough test – as opposed to the numerous unboxing and product review vlogs that will doubtless flood YouTube – I ordered one from CVP.

Overall audio quality

There are different aspects to the audio quality of such a system, including its on-board mics vs external lavs, its on-board recorder vs transmitted audio, and both the recorder and the transmitted audio vs a better system.

Using a Sound Devices MixPre-3 to provide a decent sound source into the Rode Wireless Go II transmitters

Most interesting to me was to take the on-board and external lav mics (both of which have relatively high self-noise due to their small diaphragms) out of the equation, and test the recorder and wifi alone. For this, I fed the two transmitters with a stereo signal of a simple acoustic guitar recording (recorded with a spaced pair of 7dBA Rode NT2a mics in fig 8 mode) via my Sound Devices MixPre-3 (feeding a signal from the stereo out at -6dB to give a reasonable level at the transmitters, comparable to that of the mics above). I recorded the transmitted signal via the USB out of the receiver. Here are the clips, with no processing added:

Original MixPre-3 recording:

Rode Wireless GO II on-board recorders in uncompressed/broadcast mode:

Rode Wireless GO II on-board recorders using the compressed/standard mode:

Rode Wireless GO II transmitted recording:

The verdict? Well, see what your ears say. The most obvious positive is that the Rode Wireless GO II on-board and transmitted audio show remarkably low self-noise: there is effectively no hiss in the short lead-in. The most obvious negative is the lack of bass response: OK the datasheet shows a frequency response graph with a sharp fall-off below 100Hz, but this appears to relate to the mic. Needless to say, you can boost the bass response in post, and here is a quick EQ’d version (I looked at the bass fall-off in the Rode Wireless GO II using pink noise, though my resultant EQ might be a bit too heavy – but it makes the point):

And, of course, what is effectively a high-pass filter isn’t a significant problem with intended use (speech) and will aid reduction of wind noise and other unwanted low frequencies.

So my overall view on the audio quality of the electronics? Well, the transmitted and on-board recordings sound surprisingly good: OK not up to the level of a Sound Devices MixPre-3 and not ideal for music recording, but easily good enough for use with the on-board lav mics or external lav mics (or other PIP mics such as Micbooster’s Clippy mics) for speech or ambience/nature recording, and perhaps usable – in the way that you might use a small handheld recorder – for music recording where, for whatever reason, a better and more conventional set-up wouldn’t work. Also, the compressed on-board recordings don’t sound too bad at all, despite my natural dislike of lossy compressed formats!

On-board mics

Given the mic in the original Rode Wireless GO, I was reasonably optimistic about it and, also, conscious that a) different people like different lav mics and b) I don’t own any of the more expensive lav mics (such as those made by DPA). But, for what it is worth, here’s a simple comparison of Rode’s lav mic (that’s their more expensive one – at c.£160 – and perfectly usable) vs the on-board mic recording a voice (apologies for the performance!), and recorded via the Rode Wireless GO II’s receiver (both digital out, into an Android phone running USB Audio Recorder Pro, and via the 3.5mm output into a Sound Devices MixPre-3).

Rode Wireless GO II on-board mic via digital out on the receiver:

Rode Wireless GO II on-board mic via 3.5mm analogue out:

Rode lavalier mic plugged into Rode Wireless GO II via digital out on receiver:

Rode lavalier mic plugged into Rode Wireless GO II via 3.5mm analogue out:

The verdict? The on-board lav mic is quite usable if – and this is the key – you don’t mind the transmitter being visible too. The much more secure furry windshields of the new model at least make this more feasible. And as for the difference between digital and 3.5mm output, there is little in it. Well at least with a decent sound recorder: of course, the difference will be greater if choosing between USB into a phone and analogue into a camera with poor audio.

Range and dropouts

As I said, I found the original Rode Wireless GO usable for my purposes, but I can’t deny that a more robust wifi signal wouldn’t be useful. Indeed, for many, it would be essential. The 200m line-of-sight spec for the new version (vs 70m for the original version) shows an improved wifi capability, and this is borne out even in initial, simple, testing. For example, whereas the original Rode Wireless GO – under my test conditions (a rural Norfolk village) – experiences dropouts from around 20m when worn on the rear of the subject (or ‘talent’) – i.e. blocked by the wearer’s body – the new version worn in the same way is good for about 35-40m. Obviously, different locations will produce different results, but this suggests much more suitability for, say, wedding videographers, where, of course, the recorder provides a back-up anyway. For professional sound recordists’ use (e.g. television and film) the improved signal strength is probably immaterial as the units lack the range, features, robustness and ease of control of professional wireless systems such as those produced by Audio Ltd. and Lectrosonics.

Field-recording (an update of 15.3.2020)

Rode Wireless GO II TX units in action for stereo ambience recording…

Having had the Wireless GO II for a few weeks, I’ve had a chance to use it for different scenarios, one of which is as a remote field recorder. Here the ability to use the two TX units as a remote spaced-pair of omni mics opens up all sorts of possibilities, not least recording sounds of nature (such as timid birds) from afar. Of course, if the tests above suggest that the on-board mics or the electronics aren’t are not high enough quality, you can simply use the system for monitoring: for example, running SDC mics into a Sound Devices recorder, and plugging the TX units into the recorder’s stereo out so you can hear what is being recorded from afar. Taking the Sound Devices example you could, of course, use the wireless remote control (Wingman) for the recorder too, though I haven’t tried that combination or, indeed, tested the Bluetooth range. Anyway, what I have tried out is simply recording remotely with the on-board mics, both within a Rode blimp and with their supplied fluffy windshields: of course, the former, while restricted to 35cm spacing, provides more wind protection, but the Wireless GO windshields on their own were surprisingly good and allow any spacing (in my tests this happened to be 46cm). And the fluffy windshields of the new TX units fit much more securely than those of the original Rode Wireless GO. So here are a couple of examples, one in very high wind (we had gales at the weekend) and one in slightly less windy conditions. Both just with the TX units alone and their own fluffy windshields, and simply placed in a holly tree in the garden (near the road), as in the photo above. The recordings are from the RX unit’s USB output.

Stereo ambience recording (garden in high wind):

Stereo ambience recording (garden in moderate wind):

Audio Gear DIY Projects

Primo capsules – for lav mics and DIY

February 7, 2021
A pair of the tiny Primo EM272 omni capsules: add two wires and a 3.5mm plug and you are ready to record!

Primo microphone capsules are much-loved by the DIY crowd, especially the omni EM172 (now replaced by the EM272) capsule: it is a 10mm capsule with 14dBA self-noise. As such it offers similar scope to a lavalier (lav) mic for times when you want something much smaller than a small diaphragm condenser (SDC) mic, but has much lower self-noise: lav mics typically have around 22-5dBA self-noise, which can be pretty noticeable for many recording uses, such as ambience and nature recording. The sound quality is on a par with capsules used in mid-range handheld recorders, but, of course, once you have external mics you can be much more flexible. For example the omni mics on the much-loved Sony PCM10 are too close together for stereo, so plugging in a pair of EM272 mics allows for a proper spaced pair: you can clip those to your hat, the sides of your specs or, to look slightly less silly and to avoid your head movement giving odd shifts in the stereo image, to the sides of a bag or rucksack.

And the best thing about the Primo capsules is that they are cheap. Currently in the UK an individual bare capsule is £12.78 from FEL Communications Ltd (Micboosters): FEL/Micboosters also offers various versions (e.g. pre-soldered), other Primo capsules (including cardioid and figure 8: see below), matched pairs and, for those not into DIY, capsules already made up into finished mics – their Clippy and Pluggy models. There are a couple of other manufacturers who use Primo capsules in affordable mics, the most well-known of which is LOM in Slovakia, but I think Micboosters is the only one that also sells the bare capsules: and it is one of those great small British companies, run by the very helpful Nick Roast, who has worked as a BBC sound engineer for over 30 years.

A pair of Clippy mics

I have a pair of the Clippy mics (together with Rycote furry covers that are made specifically for them), which are useful for discreet or minimalistic stereo recordings and as lower noise lav mics for dialogue. And I have used bare EM172 capsules for what Curt Olson – who inspired my experiments – calls a ‘head-spaced parallel barrier array’, albeit in my case small enough to fit inside a Rode Mk1 blimp and with some of the mic placement attributes of SASS arrays: the circular baffles are c.90mm diameter and the mics are 160mm apart. Surprisingly effective. I’ve also used an EM172 to make a boundary mic, with the capsule set off-centre in a disk of perspex (150mm diameter and 5mm thick). Perhaps next I should buy some silicon ears (I see Micboosters sell them too) and make a binaural head with a pair of EM272s, as others have done.

Primo also make a single diaphragm figure 8 capsule (the EM283), again 10mm diameter, but this is not normally available via retailers. I noticed that Micboosters had started selling them and, as I had never heard of the capsule nor could find anything about it via the internet, I bought one for the princely sum of £19.68 for fun/curiosity. The specs are not as attractive as the EM172/EM272 and the 22dBA self-noise might be rather too high for many, but it is fine when used as part of a mid-side pair for louder sources such as music or some street ambiences. I found that the EM283 capsule needs better RFI screening than the EM172 and EM272, but that’s nothing unusual. I just bunged it in an old sawn-off shotgun mic tube for testing and, though this makes the mic unnecessarily large, it is fine – all hum eliminated. At some point I’ll get around to making a smaller housing with the fine mesh screening I have bought for the job. Not entirely sure if I’ll make much use of this capsule, unlike the EM172 and EM272 ones, but it has proved useful in an odd way: I had been thinking of acquiring an AKG CK94 figure 8 mic to provide the side mic for a mid-side pair with my CK93 hypercardioid, but was worried about self-noise (the CK94 is also 22dBA) and this convinced me that for my intended use I really do need something a lot quieter (so will need to save for an MKH30). UPDATE 26.5.2021: despite my conclusions about the EM283, I did buy a used AKG CK94 after all (a bargain came along) and its theoretically identical self-noise of 22dBA is not at all problematic. Lesson learned? That not all self-noise specs are equal! I’ve written a blog post about the new mic here.

So the final word: I’d really recommend playing around with bare Primo capsules as a cheap way to learn about arrays, and, even if DIY isn’t your thing, I’d recommend a pair of ready-made Clippy mics with these capsules as a great and very affordable alternative to a pair of lav mics for those occasions when SDC mics (and P48 power) aren’t feasible.

Primo EM272 capsules as delivered: matched pair with measured sensitivity a bit better than the published specs.
A head-spaced parallel barrier array – with the influence of SASS arrays – built to fit inside a Rode Blimp.
A boundary mic with an EM172 capsule: so simple and cheap, but better performing than so many commercial offerings.
A size comparison of a Clippy mic and a miniature lav (in this case my Rode lav). The Clippy’s EM172 capsule makes it rather chunkier, but for many uses this isn’t a problem, and it is still small enough to hide under much clothing.
Experimenting with a Primo EM283 fig 8 capsule: mounting it inside part of an old shotgun mic body.
And using the Primo EM283 fig 8 mic as the side mic in a mid-side mic pair with a Rode NT55.
Audio Gear

Omni mic pair in a single blimp

January 8, 2021

I’m a fan of omni SDC pairs for outside recording. For music I will often use these in Rycote Baby Ball Gags mounted on a stereo bar, itself on a substantial stand (usually the Manfrotto 1004BAC). But where I want something more portable and more windproof, I mount the two omni mics end-to-end inside a single windshield – the Rode blimp Mk1. Joining the two mics end-to-end is easy with a rewired and drilled female-to-female xlr coupler (well, actually, the female-to-female XLR connector is actually not off-the-peg, but made up of three items: two Neutrik NM3FXI and one Neutrik KM. Neutrik’s own female-to-female XLR connector doesn’t unscrew). This places the mics  (a pair of Rode NT55 mics with the excellent NT45-O omni capsules) at a 360mm spacing, which renders a good stereo image and is exactly the ideal length for the Rode blimp (i.e. the same length as the straight part of the blimp). Being pure pressure omni mics there is, of course, no phase issue arising from the fact that they are pointing different directions.

So the end result: a simple robust set up, less fiddly and more portable than common field-recording set-ups for ORTF pairs etc. and – being all enclosed – more windproof. It’s not something I have seen or read about, but I imagine – or hope – others are doing the same.

And here’s a detail of the easily modified connector: just drill a couple of holes for the cables.

Audio Gear Audio Projects

Something (not so) nasty in the woodshed: fun with figure of eights

January 7, 2021

It has been a drawn-out project, what with Covid-19 lockdowns and restrictions, but currently I’m midway through recording an acoustic album for Norfolk singer-songwriter Luke Chapman. It’s a long way from some of Luke’s other musical pursuits, such as the stoner grunge rock Rolodex of Gods. After an initial session at Oulton Chapel (lovely acoustics), we have since been using the woodstore part of his workshop on the edge of the Barningham Hall estate: by day Luke is a woodcarver.

With a sitting position and songs with a huge dynamic range, Luke’s voice and guitar playing need the mics to give as much separation as possible between the tracks. Early tests included using a ribbon mic on his vocals (a NoHype Audio LRM-V), but I have since been using three Rode NT2a mics, all in figure-of-eight pattern so that the nulls are used to great effect to cut out spill as much as possible: the guitar mics – a stereo pair – are parallel at 300mm spacing, one aimed around the 12th fret and one towards the bridge. The results are sounding good (to our ears): the Rode NT2a is often underrated, but the HF1 capsule (also used in the Rode K2 tube mic) is quite different from the harsher capsule of the Rode NT1a and is a pretty neutral beast. And so quiet (7dBA) that you can hear the rats running around in the roof as we record. The three mics are fed through to the ‘control room’ (the main workshop) to a Sound Devices MixPre-3: simple, but effective.

I’ll post more – with some audio – as the project continues.