Trans:space

Archive for November, 2013

In trying to understand some the questions from ‘Medway Tabla’ further reading has led me here….I think it helps to answer some of them.

Monday, November 18th, 2013

Sound localization is the process of determining the location of a sound source. The brain utilizes subtle differences in intensity, spectral, and timing cues to allow us to localize sound sources.[7] Localization can be described in terms of three-dimensional position: the azimuth or horizontal angle, the zenith or vertical angle, and the distance (for static sounds) or velocity (for moving sounds).[8] The basis of localization is based on the slight difference in loudness, tone and timing between the two ears. Humans as most four legged animals are adept at detecting direction in the horizontal, but less so in the vertical due to the ears being placed symmetrically. Some species of owls have their ears placed asymmetrically, and can detect sound in all three planes, an adaption to hunt small mammals in the dark.[9]

http://en.wikipedia.org/wiki/Psychoacoustics

Evaluation for low frequencies
For frequencies below 800 Hz, the dimensions of the head (ear distance 21.5 cm, corresponding to an interaural time delay of 625 µs), are smaller than the half wavelength of the sound waves. So the auditory system can determine phase delays between both ears without confusion. Interaural level differences are very low in this frequency range, especially below about 200 Hz, so a precise evaluation of the input direction is nearly impossible on the basis of level differences alone. As the frequency drops below 80 Hz it becomes difficult or impossible to use either time difference or level difference to determine a sound’s lateral source, because the phase difference between the ears becomes too small for a directional evaluation.[citation needed]
Evaluation for high frequencies
For frequencies above 1600 Hz the dimensions of the head are greater than the length of the sound waves. An unambiguous determination of the input direction based on interaural phase alone is not possible at these frequencies. However, the interaural level differences become larger, and these level differences are evaluated by the auditory system. Also, group delays between the ears can be evaluated, and is more pronounced at higher frequencies; that is, if there is a sound onset, the delay of this onset between the ears can be used to determine the input direction of the corresponding sound source. This mechanism becomes especially important in reverberant environment. After a sound onset there is a short time frame where the direct sound reaches the ears, but not yet the reflected sound. The auditory system uses this short time frame for evaluating the sound source direction, and keeps this detected direction as long as reflections and reverberation prevent an unambiguous direction estimation.[7]
The mechanisms described above cannot be used to differentiate between a sound source ahead of the hearer or behind the hearer; therefore additional cues have to be evaluated.[8]

http://en.wikipedia.org/wiki/Sound_localization

Medway Tabla

Monday, November 18th, 2013

I wanted to use Tabla to test and explore the acoustic properties of our locations due to the variety of sounds that they are capable of producing. Tabla is the most commonly used percussion instrument in North Indian Classical music. It can produce relatively well sustained sounds (at least for a percussive instrument) as well as much shorter sounds with virtually no sustain other than the acoustic effects of the room or space it inhabits.

The following notes are just some of the sounds produced by Tabla and used as the essential learning method but also as the spoken language of Tabla.

RIGHT HAND DRUM (often referred to as the female drum).

NA or TA a sound rather like a soft cowbell but with greater sustain. (It is the most commonly used sound but is actually a harmonic of the natural pitch of the drum.
TU another sound similar to a cow bell but lower pitched and fuller.
TI a bright click similar perhaps to castanets with virtually no sustain produced by the drum itself.

LEFT HANDED DRUM (often referred to as the male drum).

GEY the bass sound of tabla with a variety of pitches created by applying pressure from the heel of the hand.
KAT a closed sound rather like a heavy clap.

Note; when both drums are played simultaneously the combined sounds have a new vocabulary. However it is not necessary to go into these just now as it may hinder rather than clarify any recognition of sounds in the recordings.

When playing Tabla it is generally believed that all the sounds should be played at a similar volume or velocity. What is interesting and particularly relevant in this investigation is that it becomes very apparent to the Tabla player that different sounds produce different volumes in varying acoustic environments.

Our environments were as follows;
PINE WOODS
We were surrounded by tall pine trees spaced roughly 5 m apart from each other and continuing for at least 80 m in any direction. A large diaphragm condenser microphone was placed roughly 2 m from the Tabla. In a studio condition we would usually be miking at around 20 cm from the instrument. However here our main objective was of course to capture the acoustic environment.
The acoustic properties of the woods were pleasing. Although the sound was not altered too greatly there was a gentle well-balanced reverb similar to a subtle artificial reverb used by music producers in studio recordings. Of particular note was the effect on the Tabla’s brightest sound ‘TI’. The sound appeared to be coming from an area some 30 or 40 m away and perhaps from a greater height. The recordings show this by way of considerably more (wet) reverb on the brighter sound than the relative dryness of the other sounds.This one sound also had the effect of greater volume than the other sounds which were relatively well balanced and unaffected by the space. WHY IS THIS?
Perhaps another point to mention would be that the space was quite beautiful and as such must have affected the perception of the music to the listener/viewer. There was a comment made, ‘this is the environment in which Tabla was designed to be played’.

SMALL CHAPEL
The room was roughly 5 m x 3 m with a low arched ceiling. All surfaces of the room were bare and it was unfurnished. A large diaphragm condenser microphone was placed roughly 2 m from the Tabla.
The acoustic properties of the room were surprisingly unpleasing according to my ears. The reverb created by the bare walls was very notable and not problematic in itself (similar to a gated reverb roughly 0.3 seconds long) but the room seemed to minimise the high and low frequencies and squeeze the sounds into the mid range. Roughly frequencies below 150Hz and above 2000Hz were constricted. The beauty of tabla of course lies in its variety of pitched and un pitched sounds which live in a band width of between 40Hz and 7000Hz but the room managed to reduce this width considerably. It could be said that the sound was ‘unmusical’.

MEDIUM SIZED HALL
The room was roughly 25 m x 15 m with a ceiling about 6 m high. There was a double door sized opening to another room considerably larger than the one we were in. The room was undergoing major refurbishment works. The surfaces were largely bare plaster work with areas of laths and straw exposed. A large diaphragm condenser microphone was placed roughly 2 m from the Tabla.

The acoustic properties of the room were very pleasing. The sounds were well balanced with natural reverbs (roughly 2 to 3 seconds long) adding warmth to the whole variety of notes produced by tabla. The bass end was thickened and enriched most notably from the sound ‘Kat’. In the woods the same hand movement on the same drum with the same velocity was very bright and you could say was interpreted by our ears at around 3000Hz. In the chapel it was heard in the mid frequencies at around 750Hz, but in this hall it sounded at around 100Hz. This is a huge difference and fascinating to witness. As the creator of the sounds the balance, warmth and long but un obstructive reverb was very friendly and exactly as I would like to listen to, or perform tabla in an acoustic environment.

SUBWAY
The subway was roughly 25 m long, 3 m wide and 2.5 m high. All surfaces were bare with each end of the tunnel fully open. I sat in the centre of the space with a large diaphragm condenser microphone placed roughly 2 m from the Tabla.

The acoustic properties of the space was as every child (big or small) would expect them to be whilst walking with stamping feet and the occasional shout or whistle. The reverb effect on all frequencies was perhaps around 4 seconds or longer but it is difficult to trace its tail due to the sound of traffic. Listening back to the recordings there seems to be a clarity of the high and low frequencies of each strike of the tabla. At the time of playing it felt like the bass end, below roughly 80Hz overpowered all other sounds when I allowed the bass sound ‘Gey’ to resonate openly. The microphone being roughly 2 m way from my ears must be the reason for this. What was most fascinating about the location was the effect on the listener and there positioning in the tunnel. It was noted that walking into the tunnel from one end, past the tabla position and then out through the other end had a very interesting effect. The low frequencies grew and overpowered as the tabla was approached and past but diminished as the distance from the instrument widened. Most interesting is the fact that immediately as the tunnel was exited the low frequencies and the effect of the reverb virtually vanished. Why would this be? I would have imagined that the reverb would have become such a part of the whole sound that it would have exited the subway in the same way that the unaffected and immidiate impact noise of the hand on the drums also travelled.

RECORDINGS
To listen to the recordings please go to:

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Four recordings have been put onto soundcloud for each of the locations. Please note the very first strike of each of the recordings as being ‘Kat’. Played in the same way and with the same velocity it demonstrates best the dynamics of each acoustic space. The differences are vast.
A further recording of the subway “Tabla Cuxton Subway Ambulant” is of great interest as it demonstrates the movement of the listener through the tunnel as mentioned above.

Glimpsing at the outside world with sound

Thursday, November 14th, 2013

My walk to work is a mix of rural and urban environments. I thought this might be a nice “experiment” and introduction to the way images are turned into sound with The vOICe (http://www.seeingwithsound.com). The vOICe takes an image and scans it from left-to-right, turning the pixels into frequencies, perceived as changes in pitch that sweep from the left to the right. I set the scanning speed at two seconds, so the first image is taken and turned into a two second long sound. Then the second and third images are also turned into sound.

Here are two sound recordings, both made of three views (images) using The vOICe to look outside while walking. Each recording is six seconds long (three images, two seconds each). Use headphones!

Listen to each, perhaps a couple of times, and form your own impression of what each sound might represent. Then, read my questions in the first comment below and answer with a following comment. Don’t peek until you first get your own impression!

vOICeOA

vOICeON

Thanks for listening (and seeing),

Michael