Better metering in the field for wildlife and field recording mono compatibility

Like most field recordists I use the metering the manufacturers give me on field recorders, and that’s fine for most stereo and binaural applications. But it does have its limitations, particularly for mono compatibility. Unlike a studio situation in the field you are recording what is out there, the only thing you can change is your physical location and the direction you are facing. Des Coulam of soundlandscapes had the concept of the sound map and using that has helped me with with urban field recordings. With bird recording it’s simple – get as close as you can to the bird without disturbing it ;) If using a directional microphone then you want to position the interference in the dead zone of the mic.

Most people on the Internet seems to listen in stereo, there aren’t going to be that many PC users hooking the output of their audio card into their 1950s valve gramophone. So binaural urban field recordings are going to be fine because if anyone listens they will be listening in stereo and most likely using headphones, which is a great mix. You get decent results even from highly reverberant recordings like the South Kensington Station pedestrian tunnel.

 

The trouble with binaural is you end up with a lot of out-of-phase signals, the classic ball of string on a goniometer studio display. With the pedestrian tunnel I tried to keep the busker central while recording, and this is serviceable in that recording. Nevertheless there are a few places where the ball of string stretches out horizontally, and mixing the signal to mono worsens the tone of the recording – the echo that was character now become colouration.

Birds are harder in binaural stereo

They are higher in pitch, and they also aren’t in a horizontal plane.

I tried hard to keep this Robin central

but I didn’t think about the vertical plane at all. You don’t, normally, because when you are recording people or anything else they are usually in front of you :)

there's also the vertical plane I didn't think of...

there’s also the median plane I didn’t think of… Swiped from here

– it was about 5m away in a tree, the vertical angle was about 45 degrees.

1412_robin_phaseThere’s about 270 degrees phase shift, hence the round goniometer display. The dominant frequency is about 4kHz, working out the path length that corresponds to that, from

velocity=frequency x wavelength

v=f×λ

so λ=v÷f , ie λ = 330/4000 = 0.08m or 8 cm. A 90 degree phase shift would be picked up from a 2cm path difference between my ears and the robin’s bill. To try and reduce this I need to be a lot more careful about orientating my head to the bird; I’m glad we don’t normally use binaural recording for birdsong from individuals 1

Unfortunately the Telinga  parabolic microphone system, in particular the DATmic also has this, because there is a baffle between the two stereo sides. One of the nice things about the Telinga is that you get the background in stereo and the wanted sound in mono.

With this swallow recording this seems to hold at the start, but drift off

It was recording using a Telinga dish and DATmic at the WSRS Ennerdale field recording meeting. The bird was sitting on a phone wire just outside the bunkhouse, I was on the first floor so roughly level with the bird about 2m away aiming out of a window. It was a handheld, snatched recording – you have to seize the moment sometimes. And I probably let the dish drift slightly.

We don’t use phase information, or interaural time differences above about 1.5kHz

Sitting at home I can hear the difference between the first part and the second part – the first part of this clip has better definition. But it isn’t easy to get this right in the field by ear alone. It appears that high-frequency stereo location above 1500 Hz is by intensity rather than phase – there seems to be some sort of phase-locking mechanism that improves low frequency discrimination by interaural phase. Which is just as well since low frequencies are masked less by the head.

Although I knew that we use both phase and intensity to derive the stereo image I didn’t appreciate the frequency dependence. This is also used in MP3 encoding, so I need to learn more about that to be able to MP3 encode field recordings better – they would lend themselves well to joint stereo modes.

This means I am sunk as far as getting the robin’s song in phase by ear. I’m just not going to hear it – I need some kind of gizmo to show me this visually.

As to whether this is practically useful in the field is another matter. Birds have a nasty habit of moving, I’m guessing a robin won’t move enough while singing to pick up an extra 2cm path length, but I don’t know.

Display technologies

A smartphone might be man enough in the processing FLOPS department to show the oscilloscope goniometer display directly, which is the non plus ultra of stereo display. But

  • I’d need to write the app
  • I only have an iPod touch and
  • the audio in is mono only

I’ll file that in the too hard department for now. There’s already more than enough to wrangle in the field and I only have two hands…

The scope display is too much to tote around, whileI do have a DS0203 digital scope, the user interface of that is fiddly and terrible. It’s acceptable on the bench and there are times you just need an isolated scope, but it would be maddening in the field.

There are three other types of stereo phase display I know of.

One is the sort of thing described in Westhost’s Project 135 – Stereo Phase Correlation meter. I’ve never seen one of these.

At the BBC they tended to measure the sum and difference levels and display these. It’s possible to do that using a single LED display by running the L+R signal to one log display and the L-R signal to another, and using bicolour LEDs, green to the L+R and red to the L-R. If you see red then there’s too much out of phase data.

The last is the Frank Fox ‘The Box’ using a square of LEDs. Oy vey – £450, I don’t think so. To go that way I need to work out how they do it, and preferably make it smaller…

The obvious place to start is with Rod Elliott/Westhost’s Project 135 – Phase Correlation Meter. It’s relatively simple and looks easy to make.

 

Notes:

  1. as can be heard in this poor recording, it’s hard to get enough discrimination against background noise with binaural. That’s just not what binaural is about, but it excels at, say a rook roost or a starling roost

The end of the road for Britain’s sound recording clubs

The Internet has done for many older forms of exchanging information – physical newspapers and magazine curculations are a shadow of their former selves. Much of this is Schumpeter’s Gale at work. it simply makes it easier to share information and ideas by disntermediating. The publishers and gatekeepers of the old world are rendered redundant. This isn’t an unalloyed win – they performed a role in screening out the rubbish, and this role has now moved to the search engines to try and make sense of the multimedia firehose pointed at your face.

the logo of the former British Sound Recording Association

the logo of the former British Sound Recording Association

People moaned that printed publications tended to favour articles that promoted their advertisers’ products. I’m not quite sure that Google adsense is necessarily a step up from that, but being able to share audio, video, images and writing all in the space of a generation is great.

The Long, Slow Vanish Of Britain’s Illustrious Recording Clubs

I came across this topic in a throwaway line in one of the Wildlife Sound Recording Society‘s newsletters, to wit

When the Society was formed, back in 1968, there were many tape recording societies around the country, today there are very a few. A google search only found one other. WSRS has stood the test of time because of the society’s specialist interest.[wildlife sounds]

Paul Pratley, WSRS secretary 2014

and Google was indeed my friend, it’s possible that Paul was already behind the times. The British Sound Recording Association closed its doors in a meeting in Oxford, to be ratified in November 2014.

NPR has a short radio piece  with a few snippets culled from the BSRA’s last meeting in Oxford in June 2014. On the face of it it this seems bizarre – in a world full of podcasters and with sound being used more and more for non-music uses it puzzles me how and where the BSRA failed to move forward. I was never a member because I didn’t see what I could learn from it, and I am not a competition guy – I have never been, either in the fields of sound recording or photography, despite the fact than I manage to take pictures and field recordings that people license. I don’t decry competitions or competing – I simply don’t understand.

This May the BSRA voted by a significant margin of 17 to 9 to wind itself up and cease operations in November.

The problem was called out over forty years ago – if sound is about all about music for you, buy a a good stereo system, not a tape recorder

Dropout called out the problem, in his valedictory column in the last issue of Tape Recorder magazine 1 issue before it became Studio Sound.

RECORDING BEGINS WITH A MICROPHONE
Recording begins, oddly enough, with a microphone ; and what your amateur recordist lacks is access to signals which are worth recording, if his interest be confined to music.
Oh, something can be done along those lines ; but how many tapes have you made which
you can replay with the kind of musical satisfaction you get from your chosen repertory
of discs? I’ll bet it’s very few ; I know it is with me.

But then, I long ago abandoned that fantasy, and began to derive my reproduced music from the radio and the gramophone. I use my recorders—three mains’ machines and a battery-portable—for other things; and when I say use, I mean use.

But, with reluctance, I have come to the conclusion that most amateur recordists have no interests with which tape can help them or—which is more likely—they have not the imagination to see what those interests might be.

Dropout, Tape Recorder magazine, April 1970

I was a child when he wrote that and never read it, but there was something magical about going out with a EL3302 cassette recorder and bringing some of the birds back in with me from the garden. The sparrows have now left my parents’ garden in London, indeed for reasons unknown they have left the city en masse.

Sparrow calls in Ipswich

It would have been nice to have had some of those old C60s with London sparrow sounds from the 1970s. Not particularly because they would have sounded that different, probably, but as a memento of flocks long gone.

The Internet has fostered a new breed of sound hunters – and phonography, sound art and field recordists are well represented. It’s not clear to me how the BSRA lost its mojo, but I admire them for having the honesty to recognise it. I do wonder if the contest mindset is perhaps an anachronism in today’s environment – the whole open-source and mashup culture of, say, freesound is a world apart from the highly structured approach of the British Amateur Recording Contest. I wouldn’t know where to start with the latter.

Notes:

  1. Tape Recorder, April 1970 page 173; you can find back issues in PDF at http://www.americanradiohistory.com/ – look for Studio Sound in Audio and Recording

Resonant sounds of London’s Museumland

iconic Queen's Tower at Imperial

iconic Queen’s Tower at Imperial

I went to university at Imperial College, in the chi-chi London district of South Kensington.  The area has much to offer the field recordist in terms of resonant public spaces. If you want to avoid the rain or simply enjoy the soundscape  you can take the long pedestrian tunnel under Exhibition Road from the tube station to the museums.

I recently returned to Imperial and went to the Alumni reception who served excellent coffee, gratis. It’s a world away from the machine coffee and plastic cups and ‘coffee whitener’ that fuelled my studies in the Physics department many years ago. The entrance to the College from Exhibition Road is now an enclosed space with lots of glass and hard surfaces, it has an interesting acoustic of its own – I recorded this space from next to the statue of Queen Mary

Footfall Foley wizards will hear the tapping aren’t high heels which most people would associate with the percussive sound but Blakeys on a man’s shoes.

South Kensington has three lovely Victorian museums. Massive galleried spaces over several floors and often a curved vaulting ceiling. These are just made for binaural stereo!

I went to the Science Museum in Exhibition Road, part of a cluster of Victorian Museum buildings. The others are the Victoria and Albert and the Natural History Museum. The latter has an amazing curved atrium and a fine acoustic space.

In the Science Museum on the ground floor near the space exhibition

the next recording is from the Energy exhibition on the second floor, looking over the massive open space to the steam engines on the ground floor

OLYMPUS DIGITAL CAMERA

the sharp snap at 00:32 is an art exhibit marked do not touch, which of course everyone touches, resulting in a spark and a slight shock to the curious.

I enjoyed the visit and the incidental soundscapes. It is also good that Britain ended its dalliance with charging for museum entry.

Apple crusher crunching sound

There’s a satisfying noise to be had from this apple crusher – the first stages of making cider

The crunch has some of the biting into an apple sound. The ripping apart sound is ever so slightly ghoulish, one for Halloween…

After this was recorded a bunch of people joined in with their kids. Kids aren’t usually conducive to easy recording, though they did a grand job turning the handle, so I switched to using a stereo contact mic on the mechanism. My contact mic has a strong magnet on it so it’ easy to get noises from ferrous metal objects.

I had to EQ out the 3kHz resonance of the mic, but the result is less satisfying than the regular recording to my ears.

The active component is this crushing mechanism

Crushing mechanism

Crushing mechanism

which turns these apples

Apples

Apples

into crushed apples ready for the press to extract the juice

crushed apples

crushed apples

Recorded with a AT8022 XY mic aimed into the hopper

 

Echoes of South Kensington Station

South Kensington Tube station is the gateway to some of London’s famous museums – the Natural History museum, the Victoria and Albert and the Science Museum. To save people getting wet or wrangling the traffic along Exhibition Road, there is a long pedestrian walkway from the station to the museums.

It has a fabulous acoustic, one that’s enjoyed by small children, buskers and field recordists alike! I went to university at Imperial College and used this tunnel often. Even now, the soundmark takes me back to student times…

Here’s the sound of a busker using the acoustic well, and some kids enjoying the tunnel later on

Robins at Alderman Canal

Part of the nature reserves series

There is a little nature reserve by the canal near the football ground, an oasis of calm. The water is sluggish with green on top apart from where the water seems to well up from the river bed in these gently roiling clear pools. I don’t think the water makes any sound here, there is some background traffic noise which would mask it.

The nature reserve was improved by the Access to Nature project in 2012. It’s easy to be cynical about some of these projects but this one seems to have worked really well, and there was a lot more birdsong in this part of path by the canal than in the unimproved bits.

Swifts getting ready to leave

Seems like it’s been a successful year for our swifts, they have been breeding and screaming parties are heard overhead.

They’re still as hard to record as they were last year, however there are more of them it seems. I got the AT XY mics on the job this time. Maybe next year I will try a seriously long boom pole to get the mic pointed straight up in the air and use the directional pattern against some of the noise and traffic rumble of the town, but I’m still of the view swifts sound best in the city!