THE BRITISH LIBRARY

Sound and vision blog

Sound and moving images from the British Library

Introduction

Discover more about the British Library's 6 million sound recordings and the access we provide to thousands of moving images. Comments and feedback are welcomed. Read more

19 September 2018

Seeing sound: What is a spectrogram?

Greg Green, Audio Project Cataloguer for Unlocking our Sound Heritage writes:

In this digital age, most of us are familiar with audio waveforms, the ‘wavy’ images that represent the dynamic course of a particular sound recording. Waveforms are in fact a type of graph, with time on the X axis and amplitude (or loudness) on the Y.

Waveform exampleFigure 1: a waveform represents a sound recording by showing amplitude over time

Waveforms are very useful for conveying basic information about a recording e.g. where the loud bits are, where the quiet bits are, and how dynamic the recording is. If you were listening to an interview, a waveform can clearly show you where someone is speaking. Unfortunately, waveforms cannot tell us much about the pitch, frequency, or harmonic content of a recording. For that we can use a different visual representation of sound… say hello to the spectrogram!

How to read a spectrogram

Spectrograms keep time on the X axis but place frequency on the Y axis. Amplitude is also represented as a sort of heat map or scale of colour saturation. Spectrograms were originally produced as black and white diagrams on paper by a device called a sound spectrograph, whereas nowadays they are created by software and can be any range of colours imaginable!

Wave form v spectragramFigure 2: waveform and spectrogram of the same recording. An oscillating low frequency buzz dominates the waveform, only the spectrogram reveals where the bird is calling

Spectrograms map out sound in a similar way to a musical score, only mapping frequency rather than musical notes. Seeing frequency energy distributed over time in this way allows us to clearly distinguish each of the sound elements in a recording, and their harmonic structure. This is especially useful in acoustic studies when analysing sounds such as bird song and musical instruments. So not only do these graphs look really cool, but they can tell us a lot about the sound without even listening.

Spectrogram example (whooper swan)Figure 3: a spectrogram showing the harmonically rich calls of whooper swans

Whooper Swan calls recorded by John Corbett (BL shelfmark WS1734 C5)

In the above example, we can see the calls of a Whooper Swan represented in a spectrogram. The fundamental frequency of the calls is at about 750Hz, which is the frequency with the most energy (usually the lowest frequency of a sound), and gives the sound its perceived pitch. Above that are the harmonics - additional, quieter frequencies that give the sound its ‘colour’ and make up a sort of sonic signature – a Whooper Swan singing a perfect ‘G’ note will have a very different harmonic structure to a piano playing that same note. This information could be used to analyse bird songs and calls in different locations, or to understand the vocabulary of a species.

Creative uses for spectrograms

Clearly spectrograms can tell us a lot about the acoustic elements of a sound, but they are not just used for scientific studies. Audio editing is most often performed with waveforms as it's easier to make cuts or process a selected time range. When editing software uses spectrograms however, it opens up a whole new realm of possibilities! With this spectral editing, we are able to look into the microscopic details of a sound and apply processes to very specific time and frequency ranges. For example, an obtrusive footstep, or car alarm could be identified and removed from a recording, just like ‘photoshopping’ sound!

Spectral repair exampleFigure 4: a recording of a robin singing was ruined by a dog barking and some low end noise – a spectrogram reveals the unwanted noises and allows the recordist to remove them.

Spectral repair BEFORE

Spectral repair AFTER

Musicians can also use spectral editing to compose and generate sounds that could not be made any other way. Patterns and shapes can be ‘drawn’ into spectrograms and played back as frequency content. In some cases, detailed graphic images can be hidden within spectrograms. Aphex Twin used this technique to hide an image of a face within the second track of his ‘Windowlicker’ EP (1999).

Aphex Face

You can find some more examples of images hidden in the spectral content of popular songs here: https://twistedsifter.com/2013/01/hidden-images-embedded-into-songs-spectrographs/

So now you know what spectrograms are, how to read them, and some of their many scientific, creative, and bizarre uses. Keep an eye out for our #SpectrogramSunday @BLSoundHeritage tweets, starting this weekend!

  UOSH_Footer with HLF logo

18 September 2018

Recording of the week: Whistling to the bujɔk - Batek fishing techniques

Coleridge Research Fellow Dr Alice Rudge writes:

The Batek are a hunting and gathering people who dwell in the lowland rainforests of Peninsular Malaysia. When visiting recently, I accompanied Batek friends on a fishing trip and was taught some new techniques.

We left early in the morning, as the river they wanted to get to was a long way from the camp, around three hours walking up and down very steep hills. As we set out, they noticed elephant tracks very close to where we were going, and when we got to the river confluence, ʔEyKtlət went ahead, and found the elephants bathing just upriver from where we had planned to go.  We changed our course and instead of following the main river, we followed one of its smaller tributaries.

DSCF5462Resting and preparing fishing rods after the long walk to the river

Batek people usually make fishing rods (bawɔl) en route to the river by scraping the leaves off palm fronds, leaving only the supple, strong stems. Fishing line and a hook is then attached to one end. For bait, people dig worms from the sides of the riverbank.

With the Batek, fishing trips usually consist of a lot of walking. Having reached the river through the forest, you then wind your way back to the camp via the water, either upstream or downstream, by wading and scrambling up and down the banks. As you walk, you fish in any suitable places that you spot.

DSCF5468Klis and NaʔBɛ̃p walking up a waterfall en route to a new fishing spot.

In one spot that we reached, NaʔSrimjam started whistling. I initially thought nothing of it. Then her sister, NaʔAliw, started whistling the exact same melody… I asked what they were whistling, and they said that they were calling the bĩl fish [unidentified] to them. We had been catching bĩl earlier, and so, knowing that they were biting that day, the sisters were whistling to attract more! They also told me there are other sounds you can do to attract certain fish to you. One of these is a kind of clicking sound made at the back of the throat, which can be used to attract bujɔk (Malay bujuk, of the family Channidae).

NaʔSrimjam evocatively described this process thus:

mɨm ʔajak bujɔk mɨʔ tɔt ʔoʔ haw prmcəm… cɨ̃t! taʔcawɔt kə=mɛt kayil, mɨʔ saŋkɛt

‘when you attract bujɔk you see it coming to get your bait, you see tiny bubbles rising to the surface of the water, then cɨ̃t [expressive of the sudden sound or feeling when a fish bites your bait]! The fish will accidentally hook itself onto your fishing hook, and you lift it out’.

I didn’t manage to record the sound while they were making it in the forest that day. I was busy fishing myself, and trying not to fall over on the slippery rocks or sink into the mud. So, the next day I went to NaʔSrimjam and asked if she would make the sounds again so I could record them.

DSCF5466Sitting down for a moment to fish

She agreed, but when she tried to whistle, the sound wouldn’t come out, and we both cracked up laughing in hysterics. She kept telling me to just do it because she was laughing too much to whistle, but I said no I wanted to record her, because she was the one who knew how to do it - I had no idea! Eventually she managed to get the sound out. I then asked her to do the clicking sound made in the back of the throat that is used to attract the bujɔk fish. After she made the sound, she then tried to teach me to do it. This meant it was my turn to make a fool of myself as I couldn’t make the sound at all. When I eventually got some sound out, we joked that it was so bad that the fish would just swim away. This whole exchange can be heard in the recording.

Sounds used to attract fish (AR_201808_STE-020)

The Alice Rudge Collection of Batek recordings is currently being deposited and catalogued, and will be held under the shelfmark C1773.

Follow @_Aliz_, @BL_WorldTrad and @soundarchive for all the latest news.

14 September 2018

Mary Jane Long

MJ Long, who died recently, was one of the key architects of the British Library. Together with her husband, Colin St. John Wilson – known as Sandy – she spent much of her career working on the development and construction of the project. Born in the United States, she studied for a Masters degree at Yale – during an era when British architects such as Richard Rogers, Norman Foster and Eldred Evans were also at Yale. She came to Europe on a study trip in the early 1960s and began working with Colin St. John Wilson shortly afterwards. Alongside her early work on the British Library – which initially was going to be in Bloomsbury – she worked on artists’ studios for Frank Auerbach, Peter Blake and R.B. Kitaj. The latter was commissioned to create a tapestry for the foyer in the British Library.

BL MJ LONG PIC

These two extracts were taken from an interview she made in 1997-98. In the first, she discusses the change of location from Bloomsbury to its current one in the Euston Road and the implications of this to both the design and the construction process. She also references the necessary collaboration of the key architects working in the practice at the time, and how architecture of this scale is rarely the hand of one person.

MJ Long describes the move from Bloomsbury to Euston (C467/26/11)

In the second, she reflects on the elements which influenced the design, and addresses challenges from those who argued that the project was so long in its gestation that the initial design originated in a different time and context.

MJ Long reflects on the design of the British Library (C467/26/09)

Blog by Niamh Dillon, Architects' Lives Project Interviewer. Architects' Lives was established in 1995 to document the life and work of British architects and their associates over the course of the 20th and 21st centuries. MJ Long was interviewed by Jill Lever for Architects' Lives in 1997-98 and her full interview can be listened to online at BL Sounds.