Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Software Tools SPICE, PCB CAD, speaker design and measurement software, calculators

Software to remove or reduce aliasing artifacts?
Software to remove or reduce aliasing artifacts?
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th July 2017, 05:48 PM   #1
mondogenerator is offline mondogenerator  England
diyAudio Member
 
mondogenerator's Avatar
 
Join Date: Sep 2009
Location: City Of Villans
Default Software to remove or reduce aliasing artifacts?

Hi.
From what I understand about aliasing, prevention is better than a cure, using LPF to cut out of band aliasing artifacts.

However I am left with a problem. Recently I have been experimenting with producing sounds in a home made synth (pcm wave table ). The aliasing artifacts it produces present themselves as what I describe as a disharmonic hiss. Not quite white noise as some subharmonics are produced. The aliasing is noticeable in the decay part of the envelope. During use the aliasing does not sound bad per se, and adds some complexity to the sound that I'd like to keep, the decay 'hiss' is the down side.

I am looking for suggestions of noise reduction software which can be 'taught' what noise is 'noise' and which can (with the help of gating) help remove the worst of the disharmonic hiss.

Many thanks for any help in advance.

Greg
__________________
Balancing the things I must do, with the things I'd like to do...This is a skill (or a luxury) amongst many that I do not possess.

Last edited by mondogenerator; 13th July 2017 at 05:50 PM.
  Reply With Quote
Old 13th July 2017, 06:56 PM   #2
Tiido is offline Tiido  Estonia
diyAudio Member
 
Tiido's Avatar
 
Join Date: Dec 2015
Location: Estonia
Send a message via ICQ to Tiido Send a message via AIM to Tiido Send a message via MSN to Tiido Send a message via Yahoo to Tiido
I think what you're hearing is quantisation noise rather than aliasing noise, most noticable with low bit width samples or output (i.e 8 bit samples).
Aliasing is the metallicness to the sound that you hear as you play higher and lower notes and it is independent of volume level, and depends on sample rate of the device and what the quality of the samples themselves are, the lower quality the more aliasing there will be.

Aliasing is removed by agressive lowpass filtering, but quantization noise is lot more difficult to deal with as it is level and sample dependent. Some combination of EQ and noise reduction can get you somewhere, in CEP you can create a noise profile from a segment in a recording and apply it in the parts that need fixing but more often than not the sound you try to doctor will get harmed more than made nicer.
__________________
Mida sa loed ? Nagunii aru ei saa :P
  Reply With Quote
Old 13th July 2017, 08:39 PM   #3
MarcelvdG is online now MarcelvdG  Netherlands
diyAudio Member
 
Join Date: Mar 2003
Location: Haarlem, the Netherlands
If it is quantization distortion, you can change it into a 4.77 dB louder white noise without distortion by means of 2 LSB peak-to-peak triangular probability density function dithering. Audacity includes triangular PDF dither, in GoldWave you have to enter an expression to get it to dither.

(Actually you can get rid of the distortion and make it only 3.01 dB louder by using 1 LSB peak-to-peak uniform probability density function dither, but then you are left with noise modulation.)

Last edited by MarcelvdG; 13th July 2017 at 08:42 PM.
  Reply With Quote
Old 13th July 2017, 09:53 PM   #4
astrojet is offline astrojet
diyAudio Member
 
Join Date: Apr 2013
Just a though, and I could be totally off-base, but when I have aliasing from undersampled time series in my daily job, I sometimes use spectral whitening around carefully chosen frequency bands and then ifft back to time domain.
  Reply With Quote
Old 15th July 2017, 06:15 PM   #5
cbdb is offline cbdb  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Vancouver
Don't know if running the sound thru a computer is an option but DSP will give the best results.

Bad Request
  Reply With Quote
Old 15th July 2017, 06:18 PM   #6
cbdb is offline cbdb  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Vancouver
Ive used xnoise before and it works quite well at learning noise.
  Reply With Quote
Old 18th July 2017, 12:11 AM   #7
Monte McGuire is offline Monte McGuire
diyAudio Member
 
Join Date: Jul 2013
Software to remove or reduce aliasing artifacts?
Quote:
Originally Posted by astrojet View Post
Just a though, and I could be totally off-base, but when I have aliasing from undersampled time series in my daily job, I sometimes use spectral whitening around carefully chosen frequency bands and then ifft back to time domain.
But, isn't the problem with aliasing that you have no way to distinguish between a properly sampled signal and an aliased artifact? I suppose if your signal is able to be predicted, and thus you really didn't need to sample the aliased material in the first place, then you could re-synthesize the stuff that got aliased from some other characteristic of the signal that you have now. But, in the general case, a sampled signal by definition only exists from -Fs/2 to Fs/2, and you have no way to know how the signal got mapped into the passband, or whether anything was the result of aliasing or not.
  Reply With Quote
Old 18th July 2017, 01:05 AM   #8
astrojet is offline astrojet
diyAudio Member
 
Join Date: Apr 2013
Agreed. In my case, I'm typically looking for stationary phases at lower-than Nyquist that are coherent between signals through time. With stacking techniques, I just need to make sure that aliased phases don't have more energy than those I care about.

My thought relating to audio signals is that this is an efficient way of reducing spikes at high frequencies. However, I'm certainly not an electrical engineer and only barely a non-rookie in diyaudio.
  Reply With Quote

Reply


Software to remove or reduce aliasing artifacts?Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
ConvolverVST is causing aliasing? keylimesoda PC Based 6 20th January 2016 08:00 PM
DACs and aliasing r010159 Digital Line Level 6 3rd June 2014 11:09 AM
What DCPs do you know that haven't got an aliasing filter? 210 Digital Source 2 20th January 2011 04:44 PM
Anti-aliasing filter requirements darkfenriz Digital Source 5 28th October 2005 01:05 PM


New To Site? Need Help?

All times are GMT. The time now is 03:25 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki