Paper #2 at SMC 2012: Noise level in IR mocap systems

Yesterday I presented a paper on motiongrams at the Sound and Music Computing conference in Copenhagen. Today I will present the paper A study of the noise-level in two infrared marker-based motion capture systems. This is a quite nerdy, in-depth study of the noise-level of two of our motion capture systems.


With musical applications in mind, this paper reports on the level of noise observed in two commercial infrared marker-based motion capture systems: one high-end (Qualisys) and one affordable (OptiTrack). We have tested how various features (calibration volume, marker size, sampling frequency, etc.) influence the noise level of markers lying still, and fixed to subjects standing still. The conclusion is that the motion observed in humans standing still is usually considerably higher than the noise level of the systems. Dependent on the system and its calibration, however, the signal-to-noise-ratio may in some cases be problematic.


  • Full paper [PDF]
  • Poster [PDF]


Jensenius, A. R., Nymoen, K., Skogstad, S. A., and Voldsund, A. (2012). A study of the noise-level in two infrared marker-based motion capture systems. In Proceedings of the 9th Sound and Music Computing Conference, pages 258–263, Copenhagen.


   Address = {Copenhagen},
   Author = {Jensenius, Alexander Refsum and Nymoen, Kristian and Skogstad, St{\aa}le A. and Voldsund, Arve},
   Booktitle = {Proceedings of the 9th Sound and Music Computing Conference},
   Pages = {258--263},
   Title = {A Study of the Noise-Level in Two Infrared Marker-Based Motion Capture Systems},
   Year = {2012}}

Norwegian Championship in standstill

NM logo

On Thursday we are organising the first Norwegian Championship of standstill at University of Oslo. This is part of the University’s Open Day, a day when potential new students can come and see what happens on campus.

Besides the competitive part, the championship is (of course) a great way to gather more data about how people stand still. The art of standing still is something that has been a great interest of mine for the last year or so, and I have been carrying out different types of smaller experiments to understand more about the micromovements observed when standing still.

For the championship we are not going down the route of asking people to stand still for as long as possible, as they do in the world record for motionlessness (the record is a little more than 30 hours). Rather, we will look at how still people can stand for 6 minutes, measured in the average speed of a motion capture marker placed on the head. The unofficial Norwegian record is 3.8 mm/s, and on Thursday we will see if anyone beats that.

The championship is open for everyone, so do come by if you are in Oslo on Thursday. The poster for the event can be seen below:

Nm Plakat 640


Yesterday Miles Phillips suggested that the word “motionlessness” may be what I am after when it comes to describing the act of standing still. He further pointed me to a web site with a list of the world records for motionlessness. The rules to compete in motionlessness is as follows:

  1. The record is for continuously standing motionless.
  2. You must stand: sitting is not allowed.
  3. No facial movements are allowed other then the involuntary blinking of the eye.
  4. Deep breathing is permitted provided it does not involve observable movement notably greater than that in normal breathing.
  5. No rest breaks are allowed at any point during the event.
  6. The venue for such an event should be such that the general public can view.

But from my point of view, being interested in micromovements, I would be very curious to see how still these record holders actually were.

At the ArtsIT conference next month I will present the results of a study on standstill that I have conducted together with Kari Anne Bjerkestrand. I have given a sneak peek of the data earlier, and below is another figure with plots of motion capture data from the study. The plots show data of a marker placed on the neck, from six different 10-minute long standstill recordings of myself and Kari Anne. It is only the vertical position of the marker that is plotted.

Arj c7 selected5

From the plots we can see that the running marker displacement was at the scale of only a few millimeters, with a maximum displacement of less than 10mm. It can be argued that this is not much, but it certainly is not absolutely still.

One thing is the quantitative data, another is our subjective experience of standing still. Even though we tried our best to stand physically still, we could easily notice how we were swaying back and forth, doing postural adjustments, etc. Observing the video recordings of ourselves afterwards, it is also possible to see these micromovements through visual inspection only.

Based on these findings, I would be very curious to see how still a person can actually stand, not only measured in hours and minutes, but also in millimeters. So to any aspiring world record breakers: please come and do your next attempt in our lab!

The act of standing still: stillness or standstill?

Plots of a neck marker from a 10 minute recording of standing still
Plots of a neck marker from a 10 minute recording of standing still

As mentioned previously (here and here), I have been doing some experiments on standing still in silence. One thing is to do it, another is to talk (or write) about it. Then I need to have words describing what I have been doing.

To start with the simple; the word silence seems to be quite clearly defined as the “lack of sound”, and is similar to the Norwegian word stillhet. There is also the broader concept of stille, which, in addition to quiet, also covers metaphorical uses of the term, e.g. calm, but I do not want to get into more trouble by using that word.

Things do not seem to be as simple when talking about the act of standing still. In Norwegian the word stillstand quite literally means “standing still”, and is clearly (and only?) describing the act of not moving. But what is the best English word to describe this? I don’t think the words inactive or immobile cover what I want to describe. So I have for the last few months used the word stillness to describe the act of standing still. However I have recently learned that this would be more of a metaphorical use of the word. For example, Wiktionary defines stillness as

  1. The quality or state of being still; quietness; silence; calmness; inactivity.
  2. Habitual silence or quiet; taciturnity.

and The Free Dictionary has an even broader definition:

  1. stillness – (poetic) tranquil silence; “the still of the night”
    hush, still
    silence, quiet – the absence of sound; “he needed silence in order to sleep”; “the street was quiet”
    poesy, poetry, verse – literature in metrical form
  2. stillness – calmness without winds
    calmness – an absence of strong winds or rain
  3. stillness – a state of no motion or movement; “the utter motionlessness of a marble statue”
    lifelessness, motionlessness
    state – the way something is with respect to its main attributes; “the current state of knowledge”; “his state of health”; “in a weak financial state”
    fixedness, immobility, stationariness – remaining in place

This is also supported by the Oxford dictionary, which suggests that the adjective still means “not moving or making a sound”. Thus, stillness seems to be too broad for my needs.

On my search in the different dictionaries I have come to realise that the word standstill might be the obvious solution to my problem. I am mainly used to this word in the context of e.g. cars standing still, but it might work also for describing human standstill. A quick search on Google Scholar mainly reveals medical or engineering papers using the word standstill, but that does not mean that it cannot be used to describe lack of human motion. In fact, searching for “standstill biomechanics” gives more than 1000 hits.

So I think my best solution is to use the words silence and standstill to describe the lack of sound and motion, respectively, and to use stillness when referring to both.

Please let me know if you have other interpretations of these words.