"Are heterodyne bat detectors crap?"

One of the interesting things about writing this blog is that the imps who run these things (any Terry Pratchett fan can tell you that all technology is actually run by tiny imps, who are usually very efficient, but can develop "attitude problems") generate clever reports that tell you about the people who look at your site: what countries they come from, what links they followed to get here and so on. An especially interesting part is what people type into Google before being directed here and it's intriguing how many people Google "bat mite" and "bat bug"!

One person recently Googled "are heterodyne bat detectors crap?" and ended up here. It's actually quite a good question and I thought I'd try to provide a relatively straightforward answer. In a word the answer is "no". However that doesn't mean they are ideal for every application. For example, for commercial bat surveys I wouldn't dream of being without a heterodyne detector, but it would be a very poor standard of survey if that was all we used. So let's consider why.

Steph Cope, a former member of our bat survey team, modelling a hand-held bat detector and digital recorder, plus the obligatory Scottish midge net! 

(Steph is now wildlife ranger at the stunning Glengorm Castle Estate on Mull)

A wise man once said that the problem with watching bats is you can't see them and you can't hear them. That's not entirely accurate, but it is basically true. Most European bat calls are ultrasonic, pitched between about 15kHz and 120kHz, depending on the bat species. For most of us 15kHz is close to the highest frequency we can hear. Our maximum varies, depending with age and gender - younger people can hear higher pitched sounds, and women usually have a higher range than men (so I get the short straw on both fronts!). So, if we want to hear bat calls we have to employ electronic means to reduce the frequency of the calls to something we can hear.

If you think back to high school physics classes you'll remember that sounds comprise a flow of waves. The more waves in a given time, the higher the frequency. So what we need is a machine that can reduce the number of waves so that we can hear the bat's call, whilst making it sound as much like the original bat call as possible. There are essentially three ways of doing this. Our unknown Googler's underlying question was probably "what is the best type of bat detector to use?" and sadly there is no perfect detector. Each of the three methods has strengths and weaknesses.

Time expansion  is the purest method and devotees of time expansion bat detectors can be more than a little evangelical about them. The bat's call is replayed at a slower rate (often ten times slower), thus reducing it's frequency. Time expanded calls tend to sound a little like bird chirps and are a perfect representation of the original bat call, making them excellent for computer-based call analysis.

Frequency Division is the third method and reduces frequency by removing a proportion of the waves, often leaving one in eight or one in ten. What is left is a "broad brush" picture of the bat call.

Heterodyne bat detectors mix the bat's call with the product of an oscillator and the two sounds together create a sound we can both hear and make sense of. They have a tuning knob, which allows you to select a frequency band to listen to. However the mixing process renders the output useless for analysis. Most better FD and TE detectors have a heterodyne detector built in as well, so you can have the ease of listening to heterodyne, whilst recording FD or TE for later analysis. A good example of this is the Bat Box Duet, which outputs heterodyne to the loudspeaker/headphones, whilst sending FD to the tape socket.

The Bat Box Duet - an excellent Heterodyne/Frequency Division bat detector.

So, are heterodyne detectors crap? No, but when selecting a bat detector you need to think about what you're going to use it for and select the type of detector that best meets your needs and budget.

Listening to bats - The cheapest bat detectors are simple FD ones, which don't need tuning and thus will allow you to hear all the bats around you without fiddling with controls. Ideal for public bat walks.

Identifying bat calls in the field- For this it is often important to identify the frequency of different parts of the bat's call and for this a heterodyne detector is best.

Confirmation of species identification - To record bat calls for later analysis you'll need either a TE or FD detector. As a general rule TE give much clearer sonograms (a graph of the bat's call, plotting frequency against time) but are much more expensive, whereas FD results in muddier-looking sonograms but are far more affordable. (TE machines are often more fiddly to use as well).

Critical species identification - I always carry a TE detector, which I don't often use, but it's ready if I come across a bat which I think might be something unusual. The high quality of sonograms produced by a TE detector mean that I'll have the best chance of identifying the calls of that special bat!

So to return to the original question "are heterodyne bat detectors crap" the simple answer is no, they're a fantastic tool but depending on what you are trying to achieve you might want a higher level of equipment.

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The Echometer EM3: The machine I love to hate

Ever since I got my hands briefly on a pre-production example of Wildlife Acoustics Echometer 3 (EM3) late last year I have been looking forward to trying one out in the field. This machine has been much discussed by professional bat-workers: a detector with heterodyne, time expansion and frequency division functionality, SD card recording and the ability to display live sonograms on a built-in screen represents a  step forward in bat survey technology. Now that I have had a few months to try one out for real I have two things to say about it:

1. Do I like it? No, I don't.

2. Would I buy one? Hell, yes.

At first sight that doesn't appear to make much sense, so perhaps I should explain...

The Echometer EM3

(Photo copyright, Wildlife Acoustics Inc)

I don't intend to recite the capabilities of the EM3. You can look that up for yourself on the Wildlife Acoustics website and in any case it would take too long. This machine is packed with functionality, and it's packed into a surprisingly small box. So I shall leave you to do your own research and tell you what I think matters.

First of all, the facility to view live sonograms (and oscillograms) is incredibly useful, allowing faster and more conclusive species identification in the field. I have long been a convert to this, having been using an Anabat-PDA combo in the field for several years. However, this has always been a large, cumbersome set-up and one that is clearly a bit of a bodge-up. It's also a bodge-up that costs an outrageous amount of money (but that's the Titley Electronics way of doing business: marry up minimum product to maximum price and factor in poor quality control for good measure!). So having the screen in a more convenient and much cheaper box should appeal to me, right? Actually, in use I found the EM3's display clarity disappointingly poor, compared to the lovely clear picture you get on a PDA screen.

In terms of functionality, the EM3 allows you to record in WAV (normal audio), WAC (Wildlife Acoustics own compressed WAV format) and also ZCA (Anabat) format. Including ZCA is great, as it means that you can use Analook to analyse calls far faster and easier than is possible using any other software. It also means that you can choose to record in a more high-fidelity mode whenever you choose to.

One of the great things about an Anabat is it's flexibility: you can use it as a handheld detector for transect work or as a passive (unattended) monitoring machine. I was expecting the same to be possible with the EM3. It is, but for some unaccountable reason you can only record in ZCA format if you also record in WAV format simultaneously. The inevitable result is that the SD card rapidly fills up with unwanted WAV files, limiting the machine's potential as a passive monitor, as it can only be used for short periods.

Wildlife Acoustics appear to have listened carefully to their customers: the machine has a number of handy and innovative gadgets. For example the ability to tag calls with a site name and user-specified labels. An interesting function is what Wildlife Acoustics have termed "Real Time Expansion" or RTE. Effectively this provides you with a Time Expansion Detector, but without the traditional problem of TE detectors: you listen to what just happened, rather than what is currently happening (TE detectors normally work by recording bat calls and replaying them to you, at around 10 times slower, thus reducing the call frequency so that you can hear it). RTE digitally reduces the gaps between the calls. so that you get the TE functionality with the advantage of continuous monitoring. Clever, though a bit weird in use.

So, why don't I like it? Well, we live in an age when electronic equipment packs more and more into the same box: many mobile phones can do a phenomenal range of tasks. Wildlife Acoustics have tried to do something similar here. But with a bat detector, it's not just about functionality - it's about the human being using it. Picture the scene: it's late at night in the middle of the bat survey season. You're tired, possibly cold and wet and you're doing your fifth survey of the week. You also face the prospect of 3 hours sleep, followed by a dawn survey. In that situation what you need is a simple-to-use and reliable detector: something that will prevent you from accidentally doing something silly and ruining your survey results. For all its cleverness, the EM3 is not as intuitive to use as I would like it to be and 5am in the morning is not time to be digging out the manual.

Now let's consider ergonomics. This may be unfair, given that the EM3's nearest competitor is an Anabat with a PDA clipped to the front, but if you're going to carry a machine in your hand for many hours you want it to FIT in your hand....comfortably. And you want all the controls to be in the right places. With all it's cleverness, the EM3 misses the boat here. It's uncomfortable to hold and awkward to use. Wildlife Acoustics would be well-advised to look at the Bat Box Duet. It's amuch simpler machine, but it's curved to fit the hand, with the frequency wheel placed exactly where your thumb sits and it's built into a solid case that you could probably play football with and still find it fully functional.

Whilst on the subject of ergonomics, the EM3's loudspeaker is poor. It's buried somewhere inside and squirts the sound away from you, instead of towards you, where you need it. With any amount of background noise it can be a struggle to listen to it. Purists will say that you should use headphones with a bat detector, as it allows you to hear and understand a bat call more easily. They're right, but when you're working alone and don't know who else might be walking about, remaining aware of surrounding noise is an important safety factor. Also, our commercial survey team use radios to keep in touch during a survey, which really wouldn't work with headphones.

To tell the truth, I don't really like the EM3: it's uncomfortable to use and hard to listen to; it feels quite cheaply made and potentially vulnerable to damage and it's just a bit too complex to be sure that a dopey, sleep-deprived mind will remember to do everything correctly.

Yet, despite that I keep finding myself taking it out on surveys. That fantastic functionality is addictive and the live sonograms are great. Okay, the screen is naff compared to an Anabat and PDA, but it fits in your pocket and no Anabat is ever going to do that, even before you erect the scaffolding to support the PDA. The bottom line is that Wildlife Acoustics have raised the bar by developing the EM3. And let's not forget that they did it for less than a grand, which is great price for a professional bat detector.

The EM3 is far from perfect and there are many things that niggle me every time I use it, but it's still impressive. Somehow it's wriggled it's way into being an essential part of my bat survey kit and if I'm honest, I'm not sure that I would part with it willingly, though I wouldn't want it to be my only choice of detector.

Wildlife Acoustics: www.wildlifeacoustics.com