Author Topic: Pls explain/elaborate more of DIGITAL ALIASING on multiFx  (Read 3287 times)

rogeryu_ph

Pls explain/elaborate more of DIGITAL ALIASING on multiFx
« on: September 12, 2009, 09:03:28 AM »
Hello guys  :)

Kindly intricate in rich detail or better explain more in layman's term what it is....How does it sound? Can one easily hear and identify it? Curious that someone can really say "So much digital aliasing sound on multifx" ???  Can someone share a link to some Digital Aliasing clip samples on the web or personal clips maybe....Thank you so much in advance. Hope this would be an eye or ear openner to anybody too.

Roger

rogeryu_ph

Re: Pls explain/elaborate more of DIGITAL ALIASING on multiFx
« Reply #1 on: September 23, 2009, 04:40:09 AM »
168 read  :icon_eek:
BUMPs UP  ???

earthtonesaudio

Re: Pls explain/elaborate more of DIGITAL ALIASING on multiFx
« Reply #2 on: September 23, 2009, 07:56:02 AM »
Try to search YouTube or elsewhere for an example of a downsampling/bitcrushing pedal.  Anything that can reduce the sample rate.  If you turn the sample rate way up, you hear your unaffected signal.  But as you start to reduce the sample rate, you start to hear odd atonal distortion products.  That's aliasing.  Basically the sample rate becomes lower than the highest frequency of your signal, but those frequencies are still coming in, so the electronics has to do something with them (it's not smart enough to just discard them), so what ends up happening is the higher signal is "read" at random points along its waveform, and a new wave is constructed from those data points which is lower in frequency and harmonically unrelated to the input signal.

For more info on aliasing, look up Nyquist and stuff about sample rates.


Now that's out of the way, I can say with reasonable certainty that when most people say "so much digital aliasing sound on multifx" they have no idea what they're talking about.  Digital multi-effect pedals may not have cutting edge sample rates and A-D/D-A converters, but generally they are fast enough to not cause aliasing (at least not audible aliasing).  However, they may have latency and phase issues that do come across as audible "weirdness."  That sort of problem will make it sound fine once its recorded, but playing it in real time will sound artificial and have a weird feel.  That's probably what most people are really talking about when they say things like that.

MoltenVoltage

Re: Pls explain/elaborate more of DIGITAL ALIASING on multiFx
« Reply #3 on: September 23, 2009, 10:26:45 PM »
Try running a Whammy 4 without distortion and you will hear all sort of aliasing, especially when you play more than one note at a time.
MoltenVoltage.com for PedalSync audio control chips - make programmable and MIDI-controlled analog pedals!

rogeryu_ph

Re: Pls explain/elaborate more of DIGITAL ALIASING on multiFx
« Reply #4 on: September 24, 2009, 11:08:33 AM »
Hi earthtonesaudio,
Ok here's what i found on youtube sample rate, nyquist frequency and aliasing... for our visual reference.
http://www.youtube.com/watch?v=Fy9dJgGCWZI

I can see he has a 10hz frequency sine wave at the top and below he said he has the sampling rate of just about 11hz frequency then he said it is below the nyquist frequency and its not apprently near to the incoming signal but when the sample rate was made double or 20 hz then it preserve the frequency content information. So meaning it need to double up the sampling rate of an incoming signal? what does it mean by below and above or slight above the nyquist frequency BTW? Sorry for such a noob mate  :) Also my digital multiFx states the its has a 44.1khz sampling frequency with 24bit A/D D/A.
I also would really much appreciate any link to give me some sample sound of this aliasing.