Sounding Lite and Top Sounding

Sounding Lite is a tool within the FIDO app designed for quick and flexible noise sample capturing from assets, pipes, and the ground using a FIDO sensor. Top sounding is a guided process within the app for accurately locating a leak between two points following a successful correlation. Both functions play an important role in any leak investigation.

Sounding Lite

Sounding Lite can be used to quickly check that a noise is still present after an overnight leak alarm. It is often used before you carry out other leak detection activities like correlation or top sounding to focus investigations on specific areas of interest. You do this by taking recordings on all the assets in the area to confirm which ones have the best sound to correlate from.

It lets you use a FIDO sensor to take audio recordings which you can listen back to, review and compare as often as you like. Each recording comes with an FFT and an STFT graph to visualize the noise profile. The app displays all the recordings you use your sensor for as a bar chart, highlighting the loudest one. Compare noise levels at different assets by simply tapping on any recording in the bar chart.

How to Carry out a Sounding Lite Session

You can use Sounding Lite with any sensor to check a noise is present, but if you are planning to use it as part of your evidence in a leak investigation it is best to launch it from a Waypoint page. Simply choose and connect to a sensor and then select ‘Sounding Lite’ from the options in the sensor menu.

Depending on how noisy the surrounding environment is, you can then choose to take either a ‘Short sample’ of 2 seconds or a ‘Long sample’ of 5 seconds. Once the recording is complete, the sound will play back automatically on a loop. We recommend listening back through headphones to hear the sound as clearly as possible. To stop the playback loop, just press ‘Stop’ in the top right corner of the screen. You can re-start it by pressing ‘Play’.

Repeat this process at all the assets where you want to take soundings. Each recording will result in a new bar on the bar chart at the bottom of the Sounding Lite screen. The bars run left to right in the order you took them so it is a good idea to note the order and locations of the assets you used so you can identify them later.

Make sure you listen back to each recording before you move on to take the next one. If one of the samples you have recorded has picked up a sound such as a lorry going past, delete it and take it again. You can delete any recording by tapping its bar on the chart and scrolling to the top of the page to press ‘Delete’. If you want to start over and delete all your recordings, then select ‘Delete all’.

Using Sounding Lite to Narrow Down Leak Noise Frequency

A useful function of Sounding Lite is the ability to really hone in on the leak noise by filtering out other noises that might be off-putting. To do this, press the blue ‘Filter Frequency Range’ slider underneath the graph and adjust the ends until you are only listening to the frequencies of interest. Doing this will filter the frequencies on all your Sounding Lite samples so you can listen for consistency across all of them. Once you are happy that the noise you are listening to is your leak, you can note the frequency range to improve the accuracy of subsequent correlations and top soundings.

You can all save your soundings by tapping ‘Save All’ in the top right corner of the screen. If you try to exit the screen without saving you will be prompted with the options ‘Exit without saving’, ‘Save all recordings’ and ‘Cancel’ in case you pressed back by accident.

Top Sounding

Top sounding is usually carried out after a successful correlation to add a further point of evidence to a leak location and narrow it down more exactly. With top sounding, you use a single FIDO sensor as a ground microphone at a series of marked out positions running along the presumed direction of the pipe, starting from the leak location identified by correlation.

If you plan to import your saved Sounding Lite frequencies to a top sounding session, you can press the small arrow in the top right corner of the Sounding Lite page. This will take you directly to Top Sounding page where your filters are already set. This option is only available if you conducted your Sounding Lite at a Waypoint.

To launch top sounding without importing Sounding Lite session frequencies, open the Waypoint page, connect a sensor and select ‘Top Sounding’ from the options menu. Top sounding sessions have a default filter range of 130-600 Hz, but you can change this manually by clicking the cog in the top right hand corner of the Top Sounding page. This opens the ‘TS Configuration’. Adjust a slider to limit the frequencies to those matching your leak. You can also change the distance between your planned top sounding locations if you want to vary it from the recommended 0.5m apart. Once you are happy with the settings, go back to the Top Sounding page using the back arrow.

How to Carry Out a Top Sounding Session

Before you can start top sounding, you need to mark the locations on the ground where you are going to take recordings. We suggest that you start at the location identified in your correlation and then make a regular mark every 0.5m along the presumed line of the pipe for a distance of 3 to 5m (around 10 feet) in each direction. Remember you can change the distance between locations by tapping the cog and telling the app the distance you prefer to use.

Once you are marked up, place your sensor on the mark nearest the asset you used as your first correlation point. In the case of a single 2-point correlation, this will have been the asset at location A. To improve accuracy, we suggest using a FIDO Top Sounding Base as this will improve the noise transmission from any ground surface. If the ground is soft and you are using the spike, attach the spike to the base and push it into the ground BEFORE you attach the sensor to avoid damaging the sensor. Also, make sure you do a cable check before inserting the spike into the ground.

Now tap ‘Record’ on the FIDO app. The sensor will immediately take a 5 second recording. Tap ‘Listen’ to check that the recording is clean and there isn’t any interference which could affect the result. If you detect any extraneous noise, simply press ‘Repeat’ to delete the sample and take a new recording at that location. Repeat this process at every marked up location along your line until you have a good quality sound recording on every point.

Once you have taken a minimum of three recordings, the ‘Process’ button will light up at the bottom of the screen. Only press this button to get your results when you have completed all your recordings. This is your top sounding result.

Understanding Top Sounding Results

Top sounding results show as three separate charts. The top chart is a series of boxes numbered left to right. The number of each box relates to the number of each recording you took in the order you took them, with number 1 being your first recording. The boxes should be gradient shaded from white to black and back to white. The black box tells you which recording had the clearest sound.

The middle chart is a graph showing how strong the noise was at various distances from the starting point to the left. This should correlate with the box chart above it to show you the exact distance from your first recording where FIDO believes the leak noise is. As with the colours in the boxes, you should notice a gradual rise and fall as the noise gets louder and then starts to dissipate.

At the bottom of the result page you will see the ‘Power Spectrum’ chart. This shows the frequency of the noise detected.

Confirming Top Sounding Results

Once you have your first top sounding result, you should carry out the same process in reverse to confirm it. To do this, take recordings at each of the locations again but starting at the marked up location furthest from your original asset. This should confirm the location from your first pass. If it doesn’t, carry out the whole process again.

Once you have your confirmed location along your marked up locations, we advise carrying out a further top sounding session running at right angles to your original line. For this final pass, start at the leak location confirmed by your first top sounding results and mark up two or three locations running away from this spot in both directions. This will help you check that the pipe is running in a straight line. For completeness, reverse the direction and carry out a final fourth pass along this perpendicular route.