In comparison to frequency division, time expansion does not involve the division of the signal but instead retains the whole waveform frequency and amplitude. This means that the full picture is there, with a high-quality sonogram and real-to-life reproduction of sound, enabling accurate analysis and the identification of species.
As the name suggests these bat detectors work by recording a short moment in time and elongating that recording by slowing it down by ten times. As a result, this lowers the frequency from ultrasonic to audible Figure 3.
The main disadvantage with this type of detector is that it essentially does not listen whilst the extraction is underway - the device is 'deaf' to bats and could miss any that happen to be passing. The individual can therefore listen in real-time and decide when a time expansion recording is most ideal. From this information, it can work out the delay between the 'crossings' the time between is referred to as the division ratio. This is recorded and the use of appropriate software can yield information on the strongest frequency components of the call over time.
The main disadvantage of these devices is that they do not capture harmonics or amplitude information. They record the loudest frequency at any one time. Timings and triggers can be controlled, however, so they are definitely useful in remote locations. They are generally used alongside software and so are often deployed for long-term static surveys, due to their ability to record lots of small chunks of data and their low power consumption.
They also reliably record every zero-crossing point - no triggers are missed. The output that the operator sees are plots showing how frequency in calls changes over time. It doesn't give the original time-amplitude information but more of an interpretation of these.
These devices are particularly unreliable for species whose harmonics vary a lot. These devices offer the ability to record continuously in real-time as per Frequency Division devices, whilst providing high-level detail much like Time Expansion devices. Because of all this detail, the file sizes can be very large so instead of recording continuously, they capture snapshots when they are triggered by predetermined frequencies and amplitude thresholds.
Perfect for environmental education where handing the public a tablets for a bat walk might not be feasible. It is intended to be used with headphones or earbuds not included. With headphones, you have a real sense of what direction the bat is coming from, aiding you in actually being able to see it. The Bat Baton has a division factor of 10, meaning the sounds of a 50kHz bat is reduced to only 5kHz—well within the range of human hearing!
These calls are captured through the microphone located at the top of the baton, and then emitted through the front-facing speaker. If you see bats at dusk, you will easily hear them with the Baton, even long after it is too dark to see.
Calls can also be recorded on other devices such as MP3 or minidisc for later analysis. The Baton is also ideal for listening to orthoptera grasshoppers and crickets whose communication is in the upper part of, or above human hearing. One PP3 9V battery lasts for up to 30hrs alkaline. Default settings have been optimized for use with the Baton. However, a bit color is required in order to save screen images as graphics files jpeg or bitmap.
They can be used for passage rates at mine entrances, etc. Likewise, they are compatible with most common sound recording apps and programs. This method works by frequency subtraction and only a very narrow part of the spectrum is scanned at any given time, so a tremendous amount information is not detected. However, many people are able to discern different species with practice in areas where there is little overlap in call frequencies.
For example, a bat heard best at 19 kHz in the eastern US is most likely a hoary bat, as calls of other species typically do not go that low. Tone qualities of the output change if the bat is calling above or below the present frequency of the detector. For example, a bat heard best at 19 kHz in the eastern US is most likely a hoary bat, as calls of other species typically calls do not go that low.
A backlit, digital display shows tuned HET frequency. This is used when actively monitoring bat activity so you can hear in real time when the detector is receiving a strong bat call.
When a suitable, desired bat has just passed by and the HET clicks are starting to fade, single-handedly stop the full spectrum recording with a button push on the back of the Dx.
It is equipped with the Pettersson, high-quality capacitance microphone which has been further improved to give lower noise, wider dynamic range and lower distortion.
This is a speciality custom microphone with each one assembled in part by Lars Pettersson himself. The recordings are second to none and is possibly the finest microphone for recording bats available in the world. The Dx can directly record pre-determined file lengths, but also can make a single recording as long as the CF card is large.
Unlike the Dx which you are limited to a 3. Each profile contains all the selectable settings such as sampling rate, triggering mode, time expansion factor and LED intensity and can be prepared in advance and saved in the detector, ready for your next session.
Spoken comments can be recorded by speaking into the microphone while recording in the direct mode, or in a special comment recording mode. The recording time is limited only by the available space on the CF-card. Time expansion factors from 1 original speed to 30 can be chosen. The recording behavior can be highly customized for any situation. The miniMIC is small, portable, and easy to carry.
If you are considering the purchase of a bat detector it may be wise to attend a few bat watching events with more experienced people and see what they are using and try them out.
Contact your Local Bat Group for details of such events and for any bat detector training sessions they may be arranging or attend a BCT training session. National Bat Helpline More information. Vat Reg No: This website places cookies on your computer to improve your experience. Identification is based on tonal quality, repetition rate and rhythm, not just on frequency. Other types of detectors are generally more expensive.
Frequency division detectors divide the incoming frequencies, usually by 10, so a 60kHz sound becomes 6kHz for example. Frequency division detectors produce a sound in real time that can be used to identify the bat on the spot although sounds can also be recorded and analysed later. Recordings made by Frequency Division detectors are not normally a very high resolution so the calls can be harder to identify than for example, with time expansion detectors. Time expansion detectors record the ultrasonic calls made by bats and play them back at a slow speed.
Calls recorded from these detectors are usually analysed on another device such as a tablet or desktop computer.
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