R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: 3rd harmonic distortion  (Read 2834 times)

Dirk Banken

  • Newbie
  • *
  • Offline Offline
  • Posts: 4
  • Real Full Name: Dirk Banken
3rd harmonic distortion
« on: February 06, 2012, 10:46:12 am »

Hello,

How much 3rd harmonic distortion is generally tolerated for a signal to be called 'clean'.  In other words: my consoles line-inputs generate 1% 3rd harmonic distortion at 31,5Hz at +24dBu according to the manual.  I'm trying to figure out what these figures mean in practice.

Thanks for your input,
Dirk
Logged

John Roberts {JR}

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 94
  • Real Full Name: John Roberts
  • 10,000+
Re: 3rd harmonic distortion
« Reply #1 on: February 06, 2012, 11:17:56 am »

Hello,

How much 3rd harmonic distortion is generally tolerated for a signal to be called 'clean'.  In other words: my consoles line-inputs generate 1% 3rd harmonic distortion at 31,5Hz at +24dBu according to the manual.  I'm trying to figure out what these figures mean in practice.

Thanks for your input,
Dirk

The perception of what is considered clean (on paper) has evolved over the years as technology gets better. Sonically what sounds clean depends on the nature of the distortion and stimulus.

Your distortion at 31Hz may be related to magnetic saturation and clean up a lot by the midrange with nominal signal levels where our hearing is more sensitive. Distortion added on top of very low bass usually sounds like more low bass, not distortion per se.

1% distortion at 1kHz is a very different animal. So answer to your question is it depends. 

JR

PS: Some people have an affection for "transformer" sound, me not so much. I don't consider 1% clean, but you are talking at near clipping levels and very low bass. Most of the music happens elsewhere.
Logged
Circular Science     http://RESOTUNE.COM

"tune it or don't play it..."

George Friedman-Jimenez

  • Newbie
  • *
  • Offline Offline
  • Posts: 11
Re: 3rd harmonic distortion
« Reply #2 on: February 06, 2012, 12:09:56 pm »

As JR is saying, harmonic distortion can be more audible at lower frequencies than the same percentage distortion at higher frequencies. To be perceived as the same loudness as a midbass note, a very low bass note has to be much louder in terms of dBSPL. For example, to be perceived as 80 phons (phon is a measure of perceived loudness), a sine wave at 90 Hz has to be about 93 dBSPL. A sine wave at 30 Hz has to be about 110 dBSPL to be perceived as 80 phon. In contrast, at 1000 Hz, an 80 dBSPL sine wave is perceived as 80 phon. This 17 dB increase in perceived loudness going from the fundamental to the third harmonic makes the distortion much more audible. See this equal volume graph: http://en.wikipedia.org/wiki/File:Lindos4.svg

1% third harmonic distortion of a 31.5 Hz fundamental means the 94.5 Hz third harmonic is 40 dB lower than the fundamental. This would only be perceived as about 23 dB lower due to the ear's lower sensitivity at low frequencies, which would correspond approximately to 7% or 8% harmonic distortion.http://www.sengpielaudio.com/calculator-thd.htm

What this means for you is that a 1% 95 Hz third harmonic of 31 Hz sounds much louder relative to the 31 Hz fundamental than, say, a 1% third harmonic of 500 Hz would sound relative to its fundamental.

I can't tell you at what percentage level the harmonic distortion would have to be for you to perceive a note as distorted. There are other factors, however, and probably the physical distortion due to changes in voice coil / magnet overlap at extreme cone displacement, and possibly cone flex at loud volumes could be as or more audible than the 1% electronic distortion in your signal. In real life, some people like the sound of distorted bass notes, probably because it occurs so commonly that we have all gotten used to it.
Logged
Pages: [1]   Go Up