BIOPAC® Systems, Inc. Logo

Amplifier module filter response times

The MP series amplifier modules incorporate a variety of filtering options. The low pass filtering options have an effect on the signal response time, which is sometimes referred to as signal delay.

Signal delay is often plotted as the function “group delay” versus frequency. This type of plot shows the typical delay the filter will have for a wide range of frequencies. The group delay plot is the derivative of the filter phase plot with respect to frequency. If the filter is perfectly linear phase, the group delay plot will be a straight horizontal line, because the derivative of a constant (linear) slope is a constant.

In practice it’s often difficult to utilize a group delay plot to get a quick and simple handle on essential filter signal delay, unless one is experienced in reading such plots. Instead, it’s typically better to show the filter response to a well-understood input signal, such as a step function.

The following plots illustrate the delay times for a variety of low pass filter settings.

10 Hz Low Pass Filter – 4 pole Besselworth
10 Hz Low Pass Filter – 4 pole Besselworth

35 Hz Low Pass Filter – 4 pole Besselworth
35 Hz Low Pass Notch Filter – 4 pole Besselworth – Notch at 60 Hz

100 Hz Low Pass Filter – 4 pole Besselworth
100 Hz Low Pass Filter – 4 pole Besselworth

500 Hz Low Pass Filter – 4 pole Besselworth
500 Hz Low Pass Filter – 4 pole Besselworth

Note that signal delay is proportional to the cut-off frequency for any particular 4 pole low pass Besselworth filter. The one minor exception is the 35 Hz LPN filter, because it consists of a 4 pole Besselworth filter and a 60 Hz Notch (band reject) filter. This additional filter adds a small additional delay.

Step Response Signal Delay (approximate)

Filter Type:

10 Hz LP

35 Hz LP

100 Hz LP

500 Hz LP

Delay at 50% (approximate):

30 ms

11 ms

3 ms

0.6 ms

Spotlight On
free BIOPAC webinar

Save the Physiology Practical Lab with BSL HOME

BIOPAC is introducing Biopac Student Lab Home (BSL HOME)—a new product specifically geared towards teaching physiology labs remotely so students can still get hands-on, practical lab experience if social distancing and stay-at-home orders keep them out of the lab..

BSL HOME will allow your students to conduct physiology labs in the safety of their own home, dorm room, or any remote location.

Watch Now!

Register Now
Latest News

BIOPAC Systems Helps STARK Industries Launch VITAL Ventilator for NASA JPL

BIOPAC’s ventilator testing equipment and expertise supports STARK Industries’ effort to manufacture, validate, and test NASA JPL’s VITAL Ventilators Goleta, California – June 16, 2020 BIOPAC Systems, Inc. announced a partnership with STARK Industries, LLC to provide ventilator validation and testing equipment for the mass production of ventilators. STARK Industries was awarded a global license […]

New Citations | Kick Off Summer with New Research in Exercise Physiology!

Comparing Muscle Movement and Involvement between Boxing Punches In the fast-paced, high-intensity combat sport of boxing, the right punch can win a fight. However, boxing is also a sport where opponents can become exhausted in mere minutes of action, and prioritizing their strength is key to winning a fight. This team recorded EMG on test […]

Read All
Request a Demonstration
Request a Demonstration