Project: Audio Induction Loop Receiver (Part 3: More Sydney Trains)

In the previous part, I had began a small project to collect samples of digital voice announcements from Sydney Trains Millenium and Warratah sets. In fact, I had continued to collect more samples just out of my own interest, but I never had the time to process them and get them site-ready. In this part, we will continue this little project, but also take a look at some of the other things I discovered along the way.

On-Platform Announcements

Cityrail’s on-platform announcements are very predictable and rigid. They begin with the standard chimes, and are followed by word-fragments which are played back at a very regular, albeit, slightly robotic cadence.

To date, capturing such announcements has been the domain of microphones, along with all the noise involved in the background. Imagine my surprise, when tripping around the network, I saw this at Macarthur.


In fact, it all became clear because it seems that Macarthur had just undergone a station upgrade, and part of that must have been fitting an induction loop transmitter for the station’s PA system. It would also explain why I was able to receive a small fragment of audio while passing through Newtown station – another newly renovated station. It seems Sydney Trains are in the process of retrofitting such equipment into designated zones on the platform to aid the hard of hearing.


The installation of the loop, of course, requires a metallic wire loop to be installed. Here, we can see the cut in the bitumen where the loop was likely installed – circling around the benches in the centre of the platform.

As a result, I was able to record my first set of samples from on-platform announcements:

I also managed to go to Riverstone, where they also have an Ampetronic sign, indicating the availability of loop audio, but I didn’t stay long enough to catch a full announcement.


In-Car Noise

I mentioned in an earlier post that the older C-sets and Tangaras, amongst others, do not carry onboard induction loop transmitters due to the electromagnetic noise the electronic control gear spews out.

Here’s some very nice samples of that:

With this very loud signal in the background, it really makes no sense to actually run any induction loop audio.

Station Names and Announcements

Around mid October, I spent some more time riding the network, which resulted in another 100-or-so audio samples. I have updated the station matrix table, with new samples added in bold.

I’ve also managed to catch the “doors closing, please stand clear” message as well.

OSCAR Set DVA Samples

Interestingly, while the above represents what users will hear when they ride the Millenium and Warratah series of trains, we also have the OSCAR sets which have a slightly different voice and cadence. I was lucky enough to board one with my equipment, but the audio amplitude was rather low, and the noise from other passengers was rather high (think mobile phones).

As a result, I only have a small limited-number of samples, which should still give you an idea of the difference in the voice between the systems.

Next Stop

This Station Is

This Train Will Stop At



There is a reassuring nature to automated, digitally synthesized announcements that play day-in and day-out. The further deployment of magnetic audio loops further improves the reach of these announcements to those of the deaf and hard of hearing, who have telecoil enabled hearing aids. It provides another way of getting the audio, albeit rather “low-fi” and simple, but it also means that anyone else who is interested doesn’t need a lot of expensive equipment to be able to resolve (and record) the signals.

Through some further dedication, I was able to improve the size of my collected audio samples to cover some more stations, on-platform announcements, and OSCAR set announcements although I think I’m not likely to have the time to collect any more samples than this.

It’s probably only something a crazy, nerdy guy like myself would do, but it’s rather fascinating to listen to the electromagnetic fields, with both intended and unintended emanations. Hope you all enjoyed it!

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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5 Responses to Project: Audio Induction Loop Receiver (Part 3: More Sydney Trains)

  1. Kerri says:

    Hi Gough!

    I think this is a great project you have undertaken here. You certainly have a lot of initiative. I particularly appreciate the way in which you have achieved such clarity with these samples. I wonder if you will please give me permission to use these samples for an experimental music project I am undertaking? I’m currently an undergraduate student studying Arts at Macquarie University.

    • lui_gough says:

      Dear Kerry,

      Of course, some samples are better than others, however, if you do find the material useful to your project, I will happily grant you permission to use it. In the case that the material is to be broadcast or widely distributed, I imagine that the rights of Sydney Trains (and the announcer, and software producer) may also be involved, to which you may have to obtain rights from as it may not be considered fair use. I have really only provided the samples as a hobby/side project to illustrate the function of the circuit as described in the experiments which I have undertaken, which I believe to be fair use.

      – Gough

  2. Chris says:

    Hi, I’m working on a university group project trying to implement a telecoil into a raspberry pi hearing aid. I didn’t quite understand how you managed to get your telecoil working. So far, you are the only person (who is not a hearing aid manufacturer) I can find who has implemented a telecoil into a receiver. Also what was the receiver? How did you listen to the recordings? was it an earphone? Thanks, Chris

    • lui_gough says:

      As I have already documented – it is already done by Silicon Chip – try to get a hold of this article if you can:

      It’s basically a magnetic induction transmission with no subcarrier. Get an inductor, amplify the output and you have a crude representation of the audio. The receiver is basically built with an Op Amp with its output, recorded by a Zoom H1 audio recorder.

      It’s hardly complex, but the switching converter on the Raspberry Pi might give you some noise.

      – Gough

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