Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

What's the effect of downsampling on the signal?

Status
Not open for further replies.

smileysam

Member level 4
Joined
Feb 19, 2006
Messages
77
Helped
12
Reputation
24
Reaction score
3
Trophy points
1,288
Activity points
1,830
Can someone clear some doubts on downsampling..
When we downsample say 2:1 .. then we are taking every 2nd sample right?
Whats the effect on the signal....(say on audio)?
Will the signal only contain lower freq components??
if i play an orig audio signal & downsampled audio sig ..what will be the diff ?


thanks alot
 

fontp

Advanced Member level 4
Joined
Nov 19, 2004
Messages
111
Helped
30
Reputation
60
Reaction score
10
Trophy points
1,298
Activity points
604
audio how to downsample

when you downsample by "taking every 2nd sample" you get low freq band sound and also highpass band aliased to lowpass band. To get right sound you should use lowpass filtering first (cut-off high pass band). The simplest way is to sum pairs of samples (CIC filter of the order 1). Or half-band filtering in analog will do
 

matrixanov

Junior Member level 1
Joined
Nov 2, 2004
Messages
15
Helped
4
Reputation
8
Reaction score
2
Trophy points
1,283
Location
Czech Republic
Activity points
124
down-sampling+wikipedia

Hi

losing high frequencies is a relative issue ,for example if you have a speech signal sampled at 44100Hz, then the new sampling frequency will be 22050 ,it means that you still have all frequencies upto 11025 Hz ,and it is more than enough for the speech signal , dont forget to use antialiasing filter with cut frequency fc=Fs/2
:D
 

cydi

Full Member level 3
Joined
Dec 12, 2006
Messages
165
Helped
14
Reputation
28
Reaction score
3
Trophy points
1,298
Activity points
2,004
downsampling

Obvious loss of quality is first effect. If you forget the LPF for antialiasing, utter loss of fidelity results!
 

bharaths_jois

Newbie level 6
Joined
Dec 28, 2006
Messages
12
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Bangalore,Karnataka,India
Activity points
1,374
downsampling theory

Down sampling or Decimation is a method to decrease the sampling frequency. Aliasing might be one of the problems that will creep in if the new sampling rate is less than the Nyquist rate. Effects of aliasing are distortion of the signal upon reconstruction.

The following link might help you.
https://en.wikipedia.org/wiki/Downsampling
 

SKS

Junior Member level 3
Joined
Nov 29, 2006
Messages
28
Helped
4
Reputation
8
Reaction score
1
Trophy points
1,283
Activity points
1,496
Re: downsampling

When using a anti-aliasing filter before DECIMATOR the high-freq components r cut-off....So here get the distortion.
 

text2babu

Member level 3
Joined
Aug 11, 2006
Messages
64
Helped
8
Reputation
16
Reaction score
3
Trophy points
1,288
Location
bengaluru
Activity points
1,708
Re: downsampling

also according to theory, after decimation ur sample will be degrated by 4, hence u should amplify the sample by more than 4 to get back the original effect
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top