Analyze sound with SpectrumView Plus

Analyze sound with SpectrumView Plus

Ambient noise consists of a mixture of individual sounds. That also applies to music. You hear it as a whole, with your brain being able to recognize individual sounds. Provided you have heard them before and therefore actually know them. There is also a range of unknown sounds. To dive into that, an app like SpectrumView Plus for iOS and iPadOS is indispensable.

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Spectrum analyzers used to be expensive and often oversized devices. The ones for high-frequency signals are still not cheap (just a fraction of what they cost in the past), spectrum analyzers for the audio spectrum are very affordable.

In fact, you can now effortlessly download it as an app on your iPhone or iPad iPad to spin. The excellent microphones of these devices pick up the entire audio range in terms of frequencies. An additional advantage of those iPhones and iPads is that the frequency characteristics of the microphones used in these devices are known. And therefore more or less calibrated in the app.

If you want to get started very seriously, there are also calibrated external microphones. However, they are not necessary – especially to just browse the audio spectrum. So it is enough to simply SpectrumView Plus) to install. As always, the larger screen surface of an iPad comes in handy to also see the smaller details.

By the way, you can also use the more limited free version first, but in this article the focus is on Plus. So if you miss an option in the free version, you know why.

Frequency Range Chart

Once the app is launched, you will see a waterfall view of the frequency spectrum. Often these types of running charts are indeed shown as a kind of waterfall flowing from top to bottom, but from right to left is actually more practical. You can then put the frequency on the x-axis of the graph and the time on the y-axis.

Then a signal is displayed at the frequency(s) it generates. The color indicates the intensity: the more towards the red, the louder. Sounds a bit spastic, but if you whistle a tune you’ll see exactly what we mean.

In any case, it is wise to initially set the range of the graph over the entire audible (and a small part inaudible in the very high and very low frequencies). To do that, tap >> in the menu bar at the bottom of the screen and then on Settings.

First put the Audio Sample Rate on 48 kHz. That is the highest achievable with the built-in microphone(s) of your iPad or iPhone and produces a maximum displayable frequency of 24 kHz. Then scroll down a bit and set the controller below Default Minimum Frequency (Hz) in view all the way to the left, and the one below Default Maximum Frequency (Hz) in view all the way to the right.

In this way, after tapping <<, the waterfall graph shows the full frequency range from 1 to 24 kHz. If you want to do it later, you can zoom in on a frequency range by using the controls just mentioned and fine-tuning them.

Does it beep or does it not beep?

Now for a practical example. Suppose you hear an annoying whistle. Such a very high pitch. Is there something wrong with your ear, or is there really a beep in the house? SpectrumView provides a very quick answer about this.

As an example, we use a tone generator to generate a tone of 16 kHz that is played through the speaker of an iPhone. The iPad – on which SpectrumView Plus runs – picks this up flawlessly. Very clearly recognizable by the continuous line in the waterfall graph.

By the way: after changing the settings or switching to another app, you must first switch SpectrumView back to live measurement mode. You do this by tapping the microphone, which can be found at the bottom left of the graph. As you can see, a very loud tone can be heard at exactly 16 kHz.

For most people (except young people and anyone who has been quite careful with their hearing) barely audible. But audible enough to be annoying. If you do hear a beep but there is really nothing to see in SpectrumView Plus, then it might be time to pay a visit to the doctor. Especially if the beep doesn’t go away on its own after a while.

Where is that beep coming from?

The question remains where a beep comes from. SpectrumView can’t really help you with that. Except that you can walk around with your iPad or iPhone and see where the sound is stronger or less strong. Then it is important to turn off all devices in the area where the sound is loudest one by one. The moment the sound disappears from the waterfall, you have caught the culprit.

For example, high-frequency beeps come from a switching power supply. Or a (defective) LED lamp, for example. In this way you can also (try to) map other disturbing and barely audible sounds.

Zoom in

As we wrote before, you can zoom in on a frequency band. You can do that via Settingsbut also by simply spreading your fingers on the part where you want to zoom in.

So you can see that we have pulled a trick here by playing a tone of 16,000 Hz and one of 15,900 Hz at the same time. In the non-zoomed view this looks like one line, zooming in shows the individual lines and thus frequencies.

On closer inspection, the single line now turns out to be a double. Sometimes such ‘behaviour’ of a source can put you on the right track of the disturbing sound.

Sound source bandwidth

You can also use SpectrumView Plus to visualize the bandwidth of your sound system (and/or the music being played). For example, if we look at the sound of an iPhone, we can see that it is cut off considerably in the higher, but also the lower frequencies.

You can determine this by zooming in on the frequencies and paying attention to the intensities. Not very surprising of course, because the speakers of a telephone are only small. It turns out those things don’t even work that bad.

Above 12 kHz, the sound intensity decreases rapidly; Zooming in on the layer shows that there isn’t much to experience there either. With a good hi-fi system you should get significantly better pictures. Of course it completely depends on the music you play. So if you want to compare, you should always do that with the same sound fragment.

‘Classic’ view

Now that you understand how SpectrumView Plus works in principle, you can probably think of many more applications. Also keep in mind that the app can also display a classic spectrogram; tap for that spec. Analyzer. The image you then see resembles what you may know from the dancing light bars on your stereo. Only now in a (much) higher resolution.

But for real analysis, the waterfall view is the most suitable. The app has many extra functions on board, including the possibility to record and more than enough settings for connoisseurs and enthusiasts. Fun to experiment with!


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