Knowledge Base

Sample Rate

The sample rate is the number of images EthoVision XT analyzes per second. Selecting a certain sample rate does not mean that the program can always analyze data at that rate. If the computer processor load is too high, EthoVision XT may skip a sample and analyze the next one. Skipped samples result in missed samples.

The maximum sample rate is the camera frame rate. The sample rate you set in EthoVision XT can only be the frame rate divided by an integer. For example, for PAL video it is 25, 12.5, 8.33, etc.

Important: Some digital cameras support very high frame rates. However, subject detection at such rates requires a lot of processor capacity. To prevent EthoVision XT from discarding samples while tracking live, do not set the frame rate and sample rate too high. Check the percentage of missed samples (see View the Detection Statistics) to make sure EthoVision XT can handle the selected frame rate.

What Is the Optimal Sample Rate?

Setting the correct sample rate is very important. If the rate is too high, the noise caused by small movements of your animal will be picked up and give an overestimate of dependent variables such as the distance moved. If the sample rate is too low, you will lose data and get an underestimate of the distance moved.

General Guidelines for the Sample Rate

We strongly recommend that you determine the optimum sample rate for your specific setup and animals (see To Determine the Optimal Sample Rate). If, for instance, your treatment causes hyperactivity, you will need a higher sample rate for hyperactive animals than somnolent animals.

Note: In the list below, the sample rate for NTSC video (29.97/s) is approximated to 30/s.

Rodents

• Rat, single subject, center-point only: 5/s
• Mouse, single subject, center-point only: 12/s
• Rat/Mouse Behavior recognition: 25–31/s (depending on TV standard)
• Rat/Mouse, three body points: 25/s (PAL) to 30/s (NTSC or digital camera)
• Rat/Mouse, three body points combined with marker-assisted identification: 12.5/s (PAL) to 15/s (NTSC or digital camera)
• Rat/Mouse, three body points combined with Deep learning-based identification: 25/s or higher. See Deep Learning: Requirements.

Other Mammals

• Tree shrew (Tupaia): 6–12/s

Fish

• Zebrafish, adult: 5–6/s
• Zebrafish larva: For analog camera: 25/s (PAL) or 30/s (NTSC). For digital camera: 30/s or 60/s. For rapid movements you may want to track with a higher sample rate. It depends on the number of tracked subjects, the video resolution, the camera settings and the processor speed of your computer whether that is possible.
• Damselfish: 5/s
• Goldfish: 0.5/s

Arthropods

• Mite: 1/s
• Parasitic wasp: 2/s
• Tick: 3/s

To Determine the Optimal Sample Rate

The optimal sample rate is the minimum sample rate that provides an accurate estimation of the dependent variables (distance, velocity, etc.) without including the redundant information due to phenomena other than the real locomotion. For example, for an animal walking in a straight line the data points will never be in a straight line because the center-point of the subject shifts laterally with each step. In order to distinguish between real movement and effects like the one described above, you can calculate dependent variables like distance moved using the maximum or a lower sample rate.

1. Create new Detection Settings and specify the maximum sample rate. Be aware that the maximum sample rate also depends on the performance of your computer, the number of animals you track, and the video resolution.
2. Acquire data with those Detection Settings.
3. Calculate the dependent variable you are interested in.
4. Export the data to Excel and plot the dependent variable values against the sample rate. In the example below, distance moved is used.