why don't we use predistortion more in the audio world?

[CopperTop]

Originally Posted by DF96

People who don't understand something will sometimes claim that it is beyond conventional analysis. That way they can either feel more comfortable in their ignorance by believing that nobody else understands it either, or they can leave the field supposedly open for their unconventional 'explanation'.

I believe you, but... presumably you will come down just as hard on anyone who still thinks that vinyl and valves are, in some mysterious way, better than digital and solid state despite all the 'conventional' evidence to the contrary? On second thoughts, probably best to let that one lie..!

[CopperTop]

Perhaps we could shift our attention from amplifiers to speakers, then? We know about (linear) room correction and so on, but can we gain anything from nonlinear correction of speakers using pre-distortion?

[tsiros]

"predistortion" is used in hifis.

it's called "equalising"

wasn't there a forumer, not too long ago, that had created an active speaker that had a ridiculously flat freq response?

[jcx]

Perhaps we could shift our attention from amplifiers to speakers, then? We know about (linear) room correction and so on, but can we gain anything from nonlinear correction of speakers using pre-distortion?

Originally Posted by jcx

...
dynamic speakers are physical performance limited "plants", sensing adds expense, economical sensors have accuracy, noise limits - so only limited negative feedback can be applied - and that really only for subs/woofers


for lots of info on dynamic speaker driver distortions, measurements, design cruise the Klippel site:

Home

specifically for a summary view of loudspeaker distortion correction try:

http://cogsys.imm.dtu.dk/nonlincomp/Klippel.pdf

and its often worthwhile poking around sites Google directs you to - to see if related material is in the higher level directories:

Symposium on Nonlinear Compensation of Loudspeakers

[DF96]

Originally Posted by CopperTop

presumably you will come down just as hard on anyone who still thinks that vinyl and valves are, in some mysterious way, better than digital and solid state despite all the 'conventional' evidence to the contrary?

I normally stay out of that debate! I use both CD and LP, and recognise that they both sound nice but different. I am cautious about dogmatic assertions by either side, as the the most dogmatic people tend to be the least knowledgeable. Note that there we are talking about a preference, quite different from the faithful amplification of a voltage signal (which is all an amp is supposed to do).

Originally Posted by tsiros

"predistortion" is used in hifis.

it's called "equalising"

Predistortion and equalisation are quite different, although the former may need to incorporate some of the latter. Equalisation is undoing the effect of a fixed linear filter. Predistortion is undoing the effect of nonlinearity, which may include signal-dependent filters.

Equalisation is relatively easy. Predistortion is harder, which is why it is generally only used when NFB cannot be used.

[tsiros]

the only good with lp is that, being analog, it doesn't require any decoding.

everything else (freq resp, noise floor, dynamic range, stereo separation) is worse when compared even to cd, let alone higher quality digital sources.

yes, it sounds different, but it is one of the very rare cases where i will insist that it is worse (when, for example, i will say that tubes sound different but not necessarily worse than ss amps)

[CopperTop]

Originally Posted by DF96

I normally stay out of that debate! I use both CD and LP, and recognise that they both sound nice but different.

Hi DF96

I can't help but notice a contradiction between your earlier dismissal of things that 'defy conventional analysis', and your use of LP. If everything is "just algebra" and open to mathematical analysis, then you should be able to 'pre-distort' (you see I'm staying on-topic!) your digital audio to sound just like an LP with none of the drawbacks, or to transfer your vinyl to digital format and perform whatever rigorous and non-hand waving processing that needs to be done to keep it sounding like vinyl. (Simply recording it 44.1/16 seems to work fine for me!)

[DF96]

Why would I want to make either one sound like the other? I also listen to FM radio - should I add a 19kHz pilot tone to my CD or put a 15kHz sharp cutoff filter on LP?

[CopperTop]

Hi jcx

So these Klippel people seem to know what they're talking about! Do you have much experience with their systems?

[jcx]

no, I just play with amplifier design - not because it is the limiting factor in audio but because thats my expertise after decades of employment designing electronics for scientific/industrial instruments

have done some motion control, designed the circuits, coded the DSP, dissed the Mech E selection of acutators, pointed out better spots for the sensors for the product performance requirements – the reason I have a little more general knowledge of Control Theory as a cross discipline subject with details, methods other EE, analog circuit designers don't often think about