Wednesday, 25 January 2017

Using the Equalisation tool

This tool is a great for reducing the levels of unwanted noise and enhancing the levels of the ones you want to keep, and it’s a great way to target certain frequencies. Again, it’s found in the Effects menu. 

Here I’m using a sonogram generated from a recording of a Siberian chiffchaff that I made with my iPhone. I’d left my recording kit at home as it was raining. It’s always the way…you find something interesting when you’re least prepared for it! Note how much darker the sonogram appear than in previous examples. I don’t know why for sure, but I suspect that this is because the mic is picking up more noise - not because it is more sensitive, but because it is not directional, so as well as the bird noise that you are trying to record, it’s also picking up background noise from all directions. 




Before you do anything else, make sure you know roughly what frequencies you want to keep/enhance. Open up the Equalisation tool and select the radial button for ‘Graphic’ towards the bottom of the window, so that it looks like the picture below. Do you remember when they made Walkmans better by adding a graphic equaliser? Well this is exactly the same, but a little more sophisticated than just allowing you to adjust the bass and the treble etc. If the blue line does not cross the graph at 0 decibels just press ‘Flatten’ to reset it. 

You’ll see that there are a series of sliding scales at the bottom the window that relate to different frequencies (hover the cursor over the button and it will tell you its frequency). It’s now simply a case of decreasing the decibels for the sounds you don't want, and increasing the decibels for the ones you do. The effect this will have on your sonogram will be to make it darker (i.e. more noise) where you have increased the decibels, and paler where you’ve decreased them. Here, I want to keep, or maybe even enhance the area around 5 khz, but reduce the rest. Your sonogram should look something like the picture below.




Now, if you like you can further refine your equalisation by be being a lot more precise in reducing the decibels close to the ones you want to keep (you can see from the graph in one of the images above that I chose quite a bit of leeway around my pretty narrow window of interest of between 4.1 and 4.7 khz).

Alternatively, you can go back to some of the other ways of noise reduction that we’ve looked at already. Here, I used the ‘Noise reduction’ tool from the ‘Effects’ menu to clear up some more unwanted noise.




What we’re left with is a much cleaner recording, but some slightly ‘fuzzy’ looking Sibe chif calls! You can take some of this fuzziness away by going back into the Equalisation tool and reducing the ‘peaks’ you’ve set on the graph, like I’ve done in the picture below. Run this twice and you’ll end up with a nice clean looking sonogram! it will play quietly when you listen to it but you can increase the volume by turning up the ‘gain’ in the box to the left of your sonogram. 








Saturday, 21 January 2017

When yellow-brows sound wrong

Sometimes Hume's warblers can be relatively easy to identify, but there are plenty of them that look pretty similar to good old fashioned yellow-browed warblers. Usually the really tricky ones can be done on plumage given good, prolonged views, but in the end with these birds, it's usually the call that finally nails the ID one way or the other, as with this bird described by Martin Garner, and this bird on Scilly, which to my eye looks very similar to a bog standard yellow-browed.

Much is made of the variation in the calls of Hume's warblers and the reliability of yellow-brows to say 'tsooweet', and I think that as a general rule, that's totally fine, However, when confronted with a tricky striped phyllosc in late autumn, it's worth remembering that not everything is set in stone. Yellow-brows frequently drop a syllable here and there among sequences of their standard calls, but how often do they give sustained bouts of consistent variant calls?

One morning in mid November 2014, Will Miles and I were birding the Nigg bay sewage works, enjoying a late fall of goldcrests and the odd chiffchaff. Andrew Whitehouse had reported a yellow-browed warbler at the site a few days previously, and it didn't take too long sifting through the crests to pick this bird up. While watching it, we were shocked to hear it give what consistently sounded like thin, high pitched monosyllabic calls. We agreed that these sounded much more like Hume's, and were audibly a decent match to a Hume's call I had on my phone. I managed to get some recordings of these while watching a bird that I considered to look like a yellow-browed warbler, with the understanding that I definitely hadn't seen it well enough to rule out something like the Scilly Hume's example above. We cautiously put the news out that the Nigg Bay YBW might be a Hume's, and sent the recording off to the Sound Approach, who also cautiously suggested that the bird might be more likely to be a Hume's warbler too.

I went back to the site at lunchtime, by now fine, sunny and warm, and picked up the same flock of crests at just about exactly the same spot. Almost instantaneously, a classic YBW call started to ring out from the flock. I was pretty sure that it was the same bird. The chances that a crest flock would host a single YBW, then a single anomolous bird, and then a single YBW again were much too slim for me, and also, based on what I'd seen, I was happy that the bird looked much better for a YBW.




Many features consistent with YBW can be seen in the photos above, including:

plenty of yellow in the supercilium
well marked dark eyestripe, particularly in front of the eye
mottled ear-coverts
no real paleness or greyish cast to the upperpart tone
dark centred greater coverts
dark bar at the base of the secondaries contrasting with strong, white greater covert bar
dark tertials with neat, narrow white fringes
The legs and feet especially were pretty pale

Along with the appearance of the bird, the calls heard at lunchtime confirmed (to me at least!) that this was a YBW. The sonogram below shows this birds calls alongside a YBW recorded on Sanday (Orkney) in September 2015. Despite the Sanday bird having a slightly wider frequency range, the calls are clearly very similar, 'V' shapes with the bottom halves 'pinched in'.


So what about the calls that fooled us so much first thing the same morning?

Well, I guess the first lesson is that a sonogram can tell you much more about a call than your ears can! Will and I were both convinced that the call we'd heard repeatedly that morning was monosyllabic, but the sonogram tells a different story, showing a very short, quick call with a similar 'V' shape to a YBW


In comparison with other calls though, these morning calls are consistently different. They only cover roughly half the frequency range of the standard YBW calls (the higher half), lack the 'pinched in' look, and they are shorter in their duration, lasting for approximately 0.2 seconds rather than the 0.3 seconds of the standard call.



The two bird theory has been suggested several times in this instance, and while it would make sense, I'm convinced there was only one stripy phyllosc present. So - was this a Hume's and we dropped the ball, or was it a weird variant YBW call?

Sunday, 15 January 2017

More ways to remove unwanted noise - Noise reduction and Pass filters

Much of the noise that you’ll want to remove from your recordings will occur across a limited frequency range, so can’t simply be cut out as demonstrated in this post. In this recording of a grey wagtail in flight, you’ll notice that the bottom half of the sonogram (the lower frequencies) is quite dark compared to the upper half (the higher frequencies). I made this recording not far from a busy road, so much of the low frequency noise will be that of cars passing by in the background.


There are three ways to reduce or eliminate this sort of noise from a recording, and all use features in the Effect menu. The tools to use are: Noise reduction, Pass filters, and the Equalisation tool. 

Noise reduction

Highlight a part of your recording that contains the noise you want to remove, but does not contain any of the important stuff you want to retain. Then select Noise reduction from the Effect menu. In the window that appears, click on the ‘get noise profile’ button.




When this is done, highlight the whole of your recording (click and drag) and then return to the Effect menu, selecting Noise reduction again. This time, just press OK and Audacity will reduce the sounds that you ‘profiled’ and reduce them across the whole recording. 



You will see in the image below that the darker area at the bottom of the sonogram has been greatly reduced.



Pass Filter

To reduce unwanted low frequencies, as with this example, choose the High pass filter from the Effect menu. 


A window will appear, and in the box labelled ‘Frequency’, type the frequency below which you want to reduce the levels. In this example I’ve typed 5000, as this is roughly where the background noise disappears, and crucially, is lower than the lowest frequency shown by the calls you’re interested in. Press OK and the High pass filter will reduce much of your unwanted noise.



You’ll be able to hear the difference in your recordings of course, as well as seeing it on the sonograms. Beware however that over editing of this sort can produce rather unnatural sounding recordings - with too much editing of this nature making recordings sound down right unpleasant. It's an effective way of cleaning up sonograms though, so if you're submitting a sonogram and a recording for a description, for instance, consider 'cleaning' the sonograms but sending a different, less edited r

Thursday, 12 January 2017

Spotted crake - daytime calls

The nocturnal 'dripping tap' call of the spotted crake is well known but no less exciting for it, and evokes images of wild, remote fenlands. Last year on my travels, I was lucky enough to spend time at a site where a pair of spotted crakes were present, and as well as being treated the rather bizarre spectacle of the pair chasing each other in flight over the marsh, I got to hear some variety in their vocalisations that I hadn't previously been aware of.

There are a few assumptions that I certainly had made about spotted crakes, mainly that they only vocalised at night, and that it was only the males that vocalised. I've found that both of these, while broadly reflecting reality, are not strictly true.



Both birds vocalise

While unfortunately I don't have any recordings to verify this, both birds were heard to 'sing' at the same time at least once, and there were numerous occasions when the locations of calls from within the site hinted very strongly towards two birds vocalising, albeit not simultaneously. The idea that both males and females can vocalise is not particularly new, but I suspect that when confronted by a singing crake, most would assume that the bird was a male. RBBP records of this species are almost exclusively attributed to 'singing males' - can this really be stated confidently? Perhaps females only vocalise when paired up? Or perhaps all those recording 'singing males' have eliminated the apparently slightly softer vocalisations of females? Whatever is going on, at sites where more than one territory is suspected, there is potential for confusion caused by singing female birds.

Day time vocalisations

One thing I really wasn't expecting was to hear the birds during the day, but in fact it wasn't particularly unusual at all. I never heard full song during the daytime (this was mostly heard in the dead of night, or around dawn and dusk), but I did hear several variations on that theme in broad daylight. These can be broken down into three broad categories, as defined below. Another aspect of these vocalisations that really surprised me was that they were not always given from within the depths of the abundant cover - birds quite frequently vocalised in the open on the edge of banks of sedge or marigold,  in full view. This gave the opportunity to watch the physical effort the birds made with each sound, standing steady and compact, heads jerking downwards with each note. In fact, the birds were surprisingly confiding during the day, and allowed themselves to be filmed through a scope (under agreement from the relevant authorities of course) if you waited quietly enough.

video

The three categories of daytime vocalisation are:

Hesitant song

This was usually heard before dusk, and could feasibly just be birds warming up, or genuinely being hesitant about advertising their position while it would still be light enough for them to worry about diurnal predators. Hesitant song basically sounds just like the standard song, but is delivered for short bursts.

Hear the 'hesitant song' here

Here, the bird threatens to get going a few times but without ever really managing it. Note how it never really finds it's rhythm too, with the pauses between notes being slightly extended from time to time. In this recording it's also clear that the singing bird doesn't enter immediately into full song, but starts off gently and ramps things up over the course of a few notes. This recording was made at around 10 pm, so late, but still fully light. The sonogram below is taken from this recording, showing the portion between 1:13 and 1:27. The 'ramping up' is visible here, with the notes noticeably reaching higher frequencies and getting louder (= darker on the sonogram) as the song progresses.



Sporadic song notes

The most frequently heard daytime vocalisation away from early mornings or late afternoons was of single or double song notes, uttered quite loud, but without ever developing into song. Perhaps these calls are used as contact calls or alarm calls? Perhaps it's exactly the same as hesitant song but with the birds being even more cautious due to the time?

Hear the 'sporadic song notes' here

Subdued song

Occasionally, during the day, birds would enter into what I have called subdued song. Here, a reasonable succession of notes are delivered, but the individual notes are given much more quietly, and never quite hit the same frequencies, or have the same quality as the full night time song. Note that the subdued song below was made from the same location as the other recordings, and the bird was at a similar distance (it must have been, as it was a very small site!). Perhaps this was the female bird singing? Whatever the reasons, you can barely hear it over the song of the skylark the my mic was pointing nowhere near, and was much further away than the crake

Hear the 'subdued song' here

I'd love to know more about these differences, and whether they're sex related, or merely products of the urge to sing, compromised by the desire not to be eaten! It must be one of the least known British breeding birds, and the opportunity to spend time in their presence was a real privilege. While they are without doubt annual breeders in the UK and probably in underestimated numbers, there are only 7 previous verified breeding attempts, apparently!  Mega!

Tuesday, 3 January 2017

Removing the sounds you don't want

Most of your recordings will feature some sound that you don’t want to keep, and there are several ways to get rid of them.  Some will be sounds you want to eliminate completely. You’ll record dogs barking, people talking, the cable hitting the mic, the clicks caused by a loose connection, and any number of other bits of unwanted noise. You can literally cut these out of your recordings with Audacity. 

At the beginning of this recording of a great tit, you’ll see some broadband (i.e. covering almost all frequencies) sound I made while rummaging around with the mic. I nearly always capture some of this noise as I have my recorder set to record sounds from 2 seconds before I actually press the button. It's set up like this to give me a better chance of getting flyovers or birds that only call once. 

To remove this, highlight the unwanted area by right clicking on the screen and dragging to highlight the area you want to remove. Then, click on the scissors icon - and your unwanted section will be removed. Note that you can only do this across all frequencies - i.e. you can’t highlight within a specific frequency range, only across a specific time period. 





The edited sonogram looks like this


Keep in mind that you’re removing some time from your recording, so the gaps between calls or song phrases will be reduced. If this needs to be addressed, you can simply copy an area from your recording of a similar length, and paste it into the right place. In my recording I’ve selected a section containing a ticking robin to maintain roughly the right period between the great tit phrases. To copy, simply select the area you want to copy in the same way you selected the section to remove. When the required area is highlighted, choose COPY from the edit menu (top of the screen). Then you just need to click where you want to insert the copied section, return to the edit menu, and hit PASTE.

EDIT - the good people at Xeno-Canto have been in touch and suggested that inserting noise from elsewhere in your recording might not be such a good idea - and have recommended adding in a silent section of the correct length instead.


Monday, 2 January 2017

Corn buntings - songs and calls

When I was a much younger person, corn buntings used to sing in the farmland that was a short walk from the end of my road, and it was a song that I remember being familiar with right back to the very earliest days of my time in birding. A lot has changed since then of course. I've moved away from the pretty, rural edge of Durham city, and of course corn buntings have moved away from pretty much everywhere. Consequently, despite North East Scotland remaining a stronghold for the species, it's a bird I hear very occasionally at best.

In November 2016 I was visiting friends near Auchnagat, in North East Scotland. After a heavy night for most, I got up at dawn and headed out, with the hope of finding and recording some tree sparrows. I hadn't bargained on stumbling into singing corn buntings - I had no idea that they sang in November (despite my earlier claims of familiarity) but here they were, several birds, perched up on fenceposts and singing as boldly as they would in spring.

Here's a recording of one of the singing birds.

http://www.xeno-canto.org/348805

And a sonogram of the song from the same recording.


Having done a little research, I've found that singing in November is not particularly unusual in corn buntings at all - which highlights how little I know about this once common bird. Another thing I couldn't say I was overly familiar with are other corn bunting vocalisations. I don't remember them from my younger years, a time when bird sounds were essentially none existent unless my dad had pointed them out to me. I've heard the distinctive calls of small groups of birds in flight on South Uist, but I encounter them so infrequently, I suspect that I wouldn't have felt too confident about nailing one in flight if I were 'out of range', especially if I were only to hear it call once or twice.

This encounter provided a perfect opportunity to listen to the calls of these birds and cement them in my minds ear. The recording below is a bird that was calling while sat up on a fencepost, and it doesn't sound noticably different to the noises that other birds were making as they flew around with a small flock of linnets. That said, this bird had just been singing and stopped as it became aware of my presence, so despite the fact that I wasn't particularly close to this bird, these calls could feasibly be alarm calls.

The calls can be heard here.

http://www.xeno-canto.org/348811

The corn bunting calls are the short, high pitched and slightly raspy sounds.


While they superficially look like quite simple calls, zooming in shows how they are composed of two distinct notes, an initial one that covers a narrow range of lower frequencies, (very) quickly followed by a second note that covers a wider frequency band, reaching up to about 8 khz. This structure can be seen in the sonogram below (I've cut out much of the sound between each call). Were talking about a gap of about 1/100th of a second between these notes, so it's no wonder that this is not clearly discernable by ear! Having heard these birds so well, and listened to the recordings, I'd now be much happier doing one solely on call if one was ever to fly over girdle ness. I'd be even happier if I got a recording that let me see this rather distinctive call structure!


While tonally, these calls sound like those that lead into the typical 'jangling keys' song, the sonogram shows a few differences (with this bird, at least!). These lead in notes are slightly lower pitched, and although appearing to have a two note structure, it's less audible (essentially due to an even smaller period between the two notes) and each note appears to cover the same range of frequencies. The lead in notes appear on the left of the sonogram below - note how the time scale in these last two sonograms differs, with the one below being even more 'zoomed in' than the one above, meaning that the horizontal axis in the one below covers a much smaller period of time.

Sunday, 1 January 2017

Audacity - the basics

There are plenty of options for birders who want to analyse and edit sound recordings, and produce sonograms depicting what they’ve heard. A decent selection can be found here and if anyone feels like experimenting we’d love to hear about what you’ve used and whether it was any good. There are two that seem to be favourites among birders, and these are Audacity and Raven. Both are free, safe to download, and are easy enough to pick up.

Audacity can be downloaded from here: http://www.audacityteam.org/  and the installation process is fairly simple - I managed it and I’m not particularly techy at all. On my mac it was a simple drag and drop followed by opening the app in my applications folder. For mac at least there are very useful instructions on the Audacity download page, and there’s no reason to expect them not to be there for Windows, Linux, or any other operating system.

Once Audacity is installed, open it up. You’ll be met with a blank grey screen with a few tool bars and menu lists at the top. It looks like a lot to take in but hopefully we’ll cover the most useful aspects of using it here, and by the time you’ve played around with it a few times, you’ll probably be confident enough to experiment yourself.

Before we get started with that though, a few boring words on file types. Your recording device will probably record sound into either .WAV or .MP3 files, or possibly something else if you've used a mobile phone (iPhones create .m4a files for example, which Audacity handles very nicely). WAV files contain the most detail but as a consequence are much bigger then MP3 - so if you want to store lots of files, email or upload your sounds anywhere, MP3 is the best bet (the lower quality is pretty much undetectable). Keep in mind that Xeno-Canto will not accept .WAV files, only MP3. So, in short, set your recorder to record MP3 files. However, Audacity cannot create MP3s directly, but it does so very effectively with the help of a plug-in called LAME. All this to say that if you want to edit your sounds and save the edited versions as MP3s then you’ll need to install this plug-in. Please don't be put off by that - it’s all very simple and Audacity will prompt you when the time comes. 

So, back to the blank grey screen. You’ve been out and recorded what you think may well have been a Siberian chiffchaff but you want to check the sonogram. Transfer your recording to your computer and save it with an appropriate name, in a place you’ll remember how to browse to. Go to the FILE dropdown menu in Audacity and choose either OPEN or IMPORT. Browse to your sound file and open - all of a sudden (unless it’s a massive file) your recording should appear in sonogram form, replacing at least some of that blank grey screen. Note - if your file does not appear in sonogram form (it might default to waveform until you tell it not to) open the dropdown highlighted in the second image and select 'spectogram'. You can play your file by hitting the green triangle button in the top left corner, stop it with the yellow square next to that, and zoom in and out of the sonogram using the magnifying glass buttons towards the right hand end of the toolbar. You can also change the shape of the window by clicking on the yellow border around the sonogram and dragging.


If you are recording in stereo you’ll note that your recording appears twice. If you want to make a nice sonogram it’s useful to get rid of one of the tracks, so click on the little black arrow that appear below the play and stop buttons. This opens up a dropdown menu, with an option to Split Stereo to Mono. Choose this option and then get rid of one of the tracks by clicking on the tiny ‘X’ in the top left corner. Once this is done you’ll be left with a single track sonogram that you can zoom in and out of, play, stop, etc. If you wanted to email it to someone or insert it into a description, you can either take a screen grab, or go to the HELP dropdown menu in Audacity, and use one of the screenshot tools.







Your first sonogram, ready to edit or use, looks like this! And unfortunately it's not the hope for Sibe but one of those mysterious 'sweeoo' chiffchaffs. Much more interesting...