Tír Na HiFi

I wanted to draw attention to this recent (Oct 2014) research http://www.sciencedaily.com/releases/20 ... 092404.htm as it has significance in a number of areas
"Barely perceptible low-frequency signals nevertheless activate measurable responses in our auditory circuits. Neurobiologists have now characterized the remarkable impact of low-frequency sounds on the inner ear."

"Further experiments will probe the possibility that this phenomenon may be linked to noise-induced auditory damage, one of the most common causes of hearing impairment in industrialized countries"

"Sources of low-frequency signals are a prominent feature of technologically advanced societies like our own. Wind turbines, air-conditioning systems and heat pumps, for instance, can generate such sounds. Hearing thresholds in this region of the acoustic spectrum vary from one person to the next. "But the assumption that the ear is unresponsive to low-frequency sounds because these are seldom consciously perceived is actually quite false. The ear indeed reacts to very low-frequency signals,"

First & foremost, I wanted to support Rocker's(?) protest about wind turbines. The search facility on this forum is really bad & let's down the whole usefulness of the info posted here (& there's some great info that has been posted)

Secondly, I suspect that this is where we should be looking for the explanations of the age old issue of why we perceive improvements but yet can't measure them. I'm pretty sure that reduction in VLF noise (Very Low Frequency) leads to major perceptual improvements in what we hear - things that I've experienced myself & I'm sure others concur - "the usual effects are much more spatial information, especially front to back, with a good recording and good gear you can hear that the trumpet layer is located to the right behind the violin player, that sort of thing"

Why are VLF measurements not usually done? Two reasons: - first it was considered that we don't perceive these signals (same as we don't perceive signals above 20KHz). Secondly, it takes a long time to run an FFT (the usual test done for analysis) for low frequency.

Anyway, thought I'd post this for both reasons above. Full paper is here http://rsos.royalsocietypublishing.org/ ... 1/2/140166

Here's a thought that could turn out to be ironic - what if the hullabaloo about high-res sounding better & yet all the measureists stating that we can't hear > 20KHz is actually to do with a difference in very low frequency (VLF) noise? In other words the relaxed digital reconstruction filters used in high-res produced less VLF noise - the opposite end of the spectrum to where they are focussed :)

jkeny wrote:I suspect that this is where we should be looking for the explanations of the age old issue of why we perceive improvements but yet can't measure them. I'm pretty sure that reduction in VLF noise (Very Low Frequency) leads to major perceptual improvements in what we hear - things that I've experienced myself & I'm sure others concur - "the usual effects are much more spatial information, especially front to back, with a good recording and good gear you can hear that the trumpet layer is located to the right behind the violin player, that sort of thing"

Why are VLF measurements not usually done? Two reasons: - first it was considered that we don't perceive these signals (same as we don't perceive signals above 20KHz). Secondly, it takes a long time to run an FFT (the usual test done for analysis) for low frequency.

Interesting article - thanks for posting. If it seems plausible that sustained low frequency noise pollutes sound reproduction by having an impact on the inner ear, I suppose a test could be done comparing a pure music signal with one including LF noise.

Rob wrote:

jkeny wrote:Interesting article - thanks for posting. If it seems plausible that sustained low frequency noise pollutes sound reproduction by having an impact on the inner ear, I suppose a test could be done comparing a pure music signal with one including LF noise.

Yes, that would be an interesting test - one would need to ensure that the original & playback system had low enough LF noise that it wasn't masking the injected LF noise. This, I believe would be the difficulty - measuring LF noise in a system (I believe it only shows with dynamic signals).

John, thanks for your post. My computer is being upgraded so my posts are via smartphone or iPad, neither being great at looking up suggested sited. When my PC is back I will read all. Thanks again.

jkeny wrote: Yes, that would be an interesting test - one would need to ensure that the original & playback system had low enough LF noise that it wasn't masking the injected LF noise. This, I believe would be the difficulty - measuring LF noise in a system (I believe it only shows with dynamic signals).

If you suspect it might be caused by digital filtering, then something like a quiet reel to reel deck might be a good option - if you think rumble would also be one of the pollutants. If you think it happens with dynamic signals then it might be something that modulates with the signal. Indeed if this issue does exist, it would be curious to know why over the years a link hasn't been noticed between the pick up of such artefacts in tests with a deterioration of sound quality.

Rob wrote:

jkeny wrote: Yes, that would be an interesting test - one would need to ensure that the original & playback system had low enough LF noise that it wasn't masking the injected LF noise. This, I believe would be the difficulty - measuring LF noise in a system (I believe it only shows with dynamic signals).

If you suspect it might be caused by digital filtering, then something like a quiet reel to reel deck might be a good option - if you think rumble would also be one of the pollutants. If you think it happens with dynamic signals then it might be something that modulates with the signal. Indeed if this issue does exist, it would be curious to know why over the years a link hasn't been noticed between the pick up of such artefacts in tests with a deterioration of sound quality.

It's very difficult to separate out noise from signal in a dynamically changing signal. It may also be that this is not an area that is investigated as it wasn't considered worth looking at.

That is a very interesting proposition, thanks for the link John.