When is Linear Phase Important?

[@hyggeligt007]

Hi Iain, thanks for the explanation! I also realized that the step response of the filter/system also benefits from a linear phase. The rising edges and falling edges also become identical, in case there is such a requirement for the said filter.

[@iain_explains]

Glad you liked it.

[@aknighton5403]

You're amazing. Thank you so much. You're truly a genius, as evidenced by the fact that though your videos are the lowest tech--no fancy simulations, just a spiral pad & ballpoint pen--they're absolutely the clearest. You communicate so well. Much appreciated.

[@iain_explains]

I'm so glad you like them! And it's great to hear that you see the value of the non-high-tech approach. So often the wow-factor of animations gets in the way of a clear explanation.

[@badalsoren2947]

sir this video has cleared lots of my doubt thank you and my gratitude to you and for all your videos

[@iain_explains]

That's great to hear.

[@rishabhkumar1050]

as always a very informative video sir

[@iain_explains]

Glad you think so!

[@knutlohmann8205]

Great thanks a lot. Is it also possible to have a constant spectrum but a non linear phase?

[@iain_explains]

Yes, that's a good question. One example is that in optical fibres the light at different frequencies travels at different speeds, but it can be with the same gain.

[@Rene_Christensen]

Yes an all pass filter will generally have constant magnitude and some nonlinear phase.

[@rudrasingh9501]

hello lian, great explanation morover can you give some examples of non linear phase system and can nonlinearity of phase be benificial in some way orother

[@iain_explains]

For example, if a communication channel has nonlinear phase (eg. optical fibre and underwater communications) or an audio signal has been received with a microphone that has a nonlinear phase response, then you will want to implement an equaliser filter with a corresponding "cancelling" nonlinear phase.

[@aarzoosingh8316]

hello sir , is it possible to equalize a system with nonlinear phase, if yes what are the problems faced during equalization of that system

[@amitpalkar934]

Iain, a lovely and nice videos. May be in next videos you can explain why for a linear phase the taps for fir filter need to be symmetric, why linear phase is difficult for IIR filters ? Do analog filters also have problems with linear phase ?

[@iain_explains]

Thanks for the suggestions. I've added them to my "to do" list.

[@stringstoparadise2392]

hello sir, hope you are fine from this video of yours i have made a few conclusions please have a look at them 1. if the wireless channel is stationary in time(without dopplers effect) then there is a constant delay between transmitter and receiver why there is destructive interference between Tx and Rx in this case there should be only constructive interference, as the delay is constant which will lead to linear phase and thus we will receive our signal without any distortion as all the frequency component of the signal will suffer same delay hence linear will be the phase

[@iain_explains]

The term "destructive interference" is not the same as "distortion". Destructive interference means that there is a second waveform (or many waveforms) that are almost completely out of phase with the main waveform (ie. in the range of 180 degrees phase-shifted). This means they will have the effect of cancelling out the main waveform. It is not related to the relationship of phase as a function of frequency.

[@stringstoparadise2392]

@@iain_explains ​ @Iain Explains Signals, Systems, and Digital Comms sir are the destructive and constructive interference addition of the copies random in nature?

[@iain_explains]

It depends on the type of channel. If it is a UTP cable with ADSL/VDSL, then the ISI comes about from bridged taps along the cable. These are different for each cable, but don't vary with time. If it is a wireless/mobile channel, then yes, the ISI is random and time varying. You might like to check out my videos on channels, ISI, fading, ... at iaincollings.com

[@clarklau1292]

Hi professor, will you consider to do paper explanation in future video?

[@iain_explains]

Sorry, I'm not sure what you're asking.

[@adams2117]

Hello, nice video! Do you have any video on halfband filter? just reading some SDR documentation and there is stated that halfband filter after DS ADC allows to bit growth from 5bits to 12bits. Never heard of such concept, maybe good topic for some video? ;)

[@iain_explains]

Thanks for the suggestion. I haven't heard of half band filters. Perhaps they are related to single side band modulation? I'm not sure. I'll check it out.

[@adams2117]

@@iain_explains "The final stage of the AD9363 is the digital conversion and decimation stage. Here the ADC will typically run at a much higher rate than the desired receive bandwidth, but the ADC itself will not provide all 12 bits defined in the specifications. The additional bits are gained in the halfband filter (HBF) stages, which will allow bit growth. The ADC itself only provides ∼ 4.5 bits of resolution. This is a typical design for sigma-delta converters (
- ADC), which inherently have low noise and run faster than the alternative successive approximation (SAR) ADCs. Refer to Section 2.5.4 for more information about
- ADCs. However, by utilizing a very high speed ADC and associated HBFs the receive signal can be digitized at 12 bits at the desired configured sample rate. Therefore, for the best signal resolution is achieved through large oversampling of the input signal and then followed by several decimation stages" www.mouser.com/pdfDocs/SDR4Engineers.pdf - page 174

[@faust-cr3jk]

Hello, two things. I wonder if linear phase and constant group delay are the same thing. Second thing, I guess that linear phase might be crucial for OFDM systems.

[@iain_explains]

Yes, that's right. Group Delay is defined as the negative of the derivative of the phase with respect to the frequency. And yes, linear phase is important for all communication systems, otherwise the equalisers become very complicated.

[@jaswanthakula8609]

Thank youu!!!!

[@iain_explains]

Glad you liked it.

[@13yroldgosu-gosu-sin24]

Is there a reason your videos are always so quiet?

[@iain_explains]

That's just the volume that my microphone puts out. Maybe I'll think about increasing it for future videos, but I don't want it to be too loud. I really want the viewer to have the feeling that I'm sitting next to them, having a considered conversation.

[@davidli7752]

@@iain_explains But lower volume will cause lower SNR of your voice due to discretization noise

[@iain_explains]

Unfortunately I don't have any control over that. That's determined by the electronics in the microphone. I'm using a fairly good quality microphone, but perhaps I should think about upgrading.

[@davidli7752]

You can run the audio through an LTI with an impulse response of 2*δ(t)