“There is a rarely heard male Asian Koel (Eudynamys scolopacea) call that I am familiar with but has been elusive to document. It is elusive in the sense that the soft call is only heard when I am near to or under the tree where the bird is.
“Unlike the more familiar melancholic “ko-el ko-el” call, which rises in pitch and finally ends in frantic desperation and then it starts all over again, this call is uttered once only.
“I had previously recorded one by chance, when I was recording the crow of a Red Junglefowl. The Asian Koel vocalised just before the crow ended – see Addendum in HERE”). Unfortunately the quality was poor as it was in a very noisy environment and the noise was heavily filtered, together with some of the wanted sound (frequencies). The loss in quality may not be evident aurally, but it shows up in sonogram.
“In this latest audio specimen, recorded as a video clip at about 7 pm on 7 Feb 2015, and then extracted as a sound clip (left and right channels), the environment was much quieter. It was unnecessary to do any audio processing other than fade-in and fade-out.
“Using the free software “Sonic Visualiser”, the waveform and sonogram of the call is shown in the image above. For this sound visualisation, the call extracted in the wav format (no data compression) was used. The call was recorded at close range, it shows that the call contains frequencies of up to about 21KHz (20,887 Hz). The waveform and sonogram are shown with left and right channels combined as one.
For comparison, I did the same sound visualisation using the mp3 format of the audio file, which is shown in the attached pic (above). The waveform and sonogram are similarly shown with left and right channels combined as one as the wav format version.
The most obvious difference between the two sonograms is that frequencies of the call above 16KHz has been removed by mp3 data compression. This is a well known algorithm of mp3 compression to reduce the file size.
Another sound visualisation using the free software “Sonogram Visible Speech” is shown above. This software does not support mp3 format so I can’t do a corresponding comparison between the two audio formats.
Nonetheless, “Sonogram Visible Speech” support 3D perspective of a sonogram, where the height of the “mountain” represents the loudness of the corresponding frequencies at a specific time. The 3D sonogram of the call is shown above.
“For those who may be interested to try it out, the free version of “Sonogram Visible Speech” is no longer available for download. Only paid version is available now.
“Finally, below is the video of the rare call together with sound visualisation shown in real time:”
Sun Chong Hong
2nd February 2015