Axiom Home Page Forums General Discussion Technical Questions Harmonics above 20khz

Thought some you might find this interesting:

http://www.its.caltech.edu/~boyk/spectra/spectra.htm

I was about to say "Big deal. Yeah, we know that many instruments have harmonics way above our hearing threshhold." I was also about to stop reading, but then I got to section X where it talks about the Japanese listening tests using a ultra-tweeters and EEGs attached to the listeners.

Makes you wonder.

Does this mean instantaneous A/B comparisons may not be the way to go when comparing speakers/gear?

That one had me scratching my head, too.

Yes, but there doesn't appear to be any instance in the literature where Oohashi's brain-wave results were confirmed by other investigators. In any case, an unconscious brain-wave isn't hearing, and that's what we work with.

Dr. Toole has discussed this in Sound Reproduction and at p.443 refers to the work of Plenge et al where a difference between a 15KHz and 20KHz cutoff was inaudible and the more recent paper subsequent to that of Oohashi where Nishiguchi et al found no audible results in ultra-high frequencies(this one is available online here ). He also comments on the somewhat related study by Meyer and Moran, which has been discussed here in the past, which showed that running excellent quality SACDs and DVD-As through a 16 bit/44.1KHz A/D/A conversion, thereby "downgrading" them to the regular CD standard, made no audible difference in their excellence.

I'm not sure what I think of that whole downgrading to show the difference (or lack thereof) between SACD/DVD-A versus CD. It seems like it shows that that particular conversion process works without degrading the sound, but it doesn't really show that material mastered for the different formats sounds the same. I'm not claiming there are differences to be heard so much as I'm arguing that they should have stronger footing for their case, which means SACD/DVD-A versus CD directly, not a simulation of one of the formats that's theoretically equivalent.

No, Charles; often they aren't the same. The study specifically points out that many SACDs and DVD-As are superior to CDs in sound quality. The point is that when there's a superiority it's due to better recording , mixing, mastering, not more bits or a higher sampling rate. The only way to clearly demonstrate this is with the superior SACDs/DVD-As played "full-strength" and then with the 16bit/44.1KHz CD limit applied. Playing a CD as such in comparison would be meaningless, as even a CD of the same performance often undergoes different production values.

I understand that they're often mixed differently. My only point is that a filter isn't a CD. The arguments are strong for it being a fair representation of the CD format, but it just strikes me as cutting corners to make the comparison.

While I was reading I kept thinking, Why isn't this being done an anehoic chamber to cut down on any possible issues with room harmonics.

CV, how would that be cutting corners if that's exactly how a lot of modern source material is converted before mastering to CD? Master tapes are usually of higher resolution than the CD format can handle.

When I read this I couldn't help but think of wine testing, where the testers use some type of food to clear their pallet before testing another wine or where in a fragrance shop, they use a cup of coffee beans to help clear your 'bias' of the first scent. It makes sense in some ways to pause in an A/B test but it also makes sense to switchover quickly as I found, at least, I could hear huge differences between some speakers. Maybe the key is too A/B switch quickly, like most do, to narrow down your choices, then to listen more leisurely/critically on your final selections (I guess that's what most of us did).

Very interesting.

My first reaction was like Peter's - you can't HEAR that stuff, so it doesn't matter if it exists or not. If a note is played in the forest but it's inaudible, it doesn't matter if there is anybody there to hear it.

The brain wave thing is interesting, but I'm not sure it's compelling. Even if your ears are transmitting a signal to your brain at those frequencies (a claim of which I remain dubious), that doesn't necessarily mean that you are PERCEIVING those signals.

Note the bold. No matter if it's theoretically a perfect representation, it's not a CD, and there can always be arguments made (admittedly weak) that it's not showing the sum of differences between formats. To eliminate all doubts is to have actual SACDs and DVD-As versus actual CDs. Otherwise, it's cutting corners, or are we just not as anal about such details as the tweak faithful?

I'm of the opinion that a D/A converter doesn't care where the digital stream is coming from before it sends the analog info along to the amp.

It's a fair opinion, and it's one I share. It simply seems like an unnecessary difference to leave in. I suppose the real point is that it's not SACD/DVD-A versus CD, but higher resolution audio versus lower resolution, and in that case, there's no need to bring those formats into it at all.