🚀 go-pugleaf

>The point is that other than people who've been listening via
>monitoring systems with lots of high frequency nonlinear distortion,
>*nobody* can hear the difference these filters make until the corner
>frequency is below 16 KHz.
>
>There is BTW a well-documented psychoacoustic reason for this which
>I've mentioned on several newsgroups several times and I don't think
>there is any informed controversy over. Above about 12 KHz human
>adults have one critical band. It tends to be captured by the lowest
>frequency and strongest sounds in its frequency range. The nature of
>musical program material is that there is plenty of content below 16
>KHz to do that. Since the critical band is dominated by the content
>below 16 KHz, the presence or non-presence of content above 16 KHz is
>not perceived.
>
>
Well, what if pre-ringing is below 12KHz? You�re arguiing about
amplitude, I argue about phase.

>Mr. Grasso writes:

Call me Grasso, Uli the Grasso, Uli, Ulrich, Mr. Grassberger, but
please not Mr. Grasso.
>
>"The reason is that: If aliasing will occur not until 48KHz the
>lowpass filters can be made much simpler and softer. The way in which
>signals over 20KHz are cut off in today A/Ds, D/As and resampling
>filters is brute: Linear-phase filters lead to pre-ringing, an effect
>which is absolutely impossible in the analogue world (in the nature
>physics that our ears are made for), that is alien stuff. "
>
>Pre-ringing seems to happen with musical instrument sounds, not just
>test signals. Musical instrument sounds in the last audible octave
>come from lightly-damped resonators that take a decent number of
>cycles to build up their resonance, but the still seem to be able to
>stimulate pre-ringing, albeit at pretty low levels.
>
Yor�re right. I didn�t take this into account, at least not for all
the time I was working on that paper. Anyway, would you say that
distortions are unimportant because instruments produce them anyway? 

>Anybody who wants to can download this file:
>http://www.pcabx-pro.com/technical/reference/triangle-2_2496.wav and
>take a look at it with a 24/96 wave file editor. This file was
>created using a pair of B&K 4007 measurement mics, an Audio/Technica
>48volt phantom power supply, a pair of Benchmark Media MP2 mic pre (r
>esponse to 200 KHz), and a CardDeluxe running at 24/96.  There is
>about 4 milliseconds of background noise before the striking of steel
>on steel.  The left channel peaks at 0.00375 seconds from the
>beginning of the file and the right channel peaks about 0.00390
>seconds. OK the triangle was not perfectly centered between the two
>mics.
>
>OK, now lets downsample this file to 1644 with some nice brutal
>brickwall filtering. That file is called
>http://www.pcabx-pro.com/technical/reference/triangle-2_1644ds.wav  .
>If you compare the first 4 milliseconds of the two files you can see
>that all sorts pre-ringing is taking place in the downsampled files.
>
>OK so here is the challenge. Prove the  pre-ringing is audible by
>just listening to the two files, no peeking!
>
>I don't think anybody is going to walk way with the prize on this
>one. 

I didn�t try to *prove* that pre-ringing of digital audio is
perceptible. That paper is an opinion, and it fits into the generally
rebellic style of my site.

>The reason is clear to anybody who understands backwards
>temporal masking. Here's a reference:
>http://www.umiacs.umd.edu/~desin/Speech1/node11.html

Esin Darici Haritaoglu says that signal one will mask signal two in
the same "critical band", but nothing about the perceptible quality
(f.e. stereo direction) of signal one.

>"Analogue tape machines are very sensitive for high amplitudes at
>high frequencies, the dynamic range drops down dead if 20KHz is to be
>recorded with -20dB on a cassette recorder."
>
>That would be pretty irrelevant to 15 ips or 30 ips master tapes,
>wouldn't it?
>
CDs aren�t recorded on 15ips tape often.

>"Therefore, when CDs were invented twenty years ago the minimum
>filter steepness was standardized with 50dB fall in a few half-tones.
>(...approximately - I don�t have the papers handy now.)"
>
>Yes, brick wall filters have been around for quite a while. Aliasing
>is pretty nasty sounding stuff. 

But ultra-high frequency "dirt" is not the same as aliasing.

>"To show you another point on that field: The HF modulation frequency
>in analogue tape machines is higher than 80KHz, simply because it
>needs to be that high for a smooth upper end."
>
>The major benefit of high bias is that it minimizes intermodulation
>products that might otherwise fall in the normal audible range, not
>smoother high frequency response.
>
When I wrote "smooth" I also meant this in a figurative sense,
"clean". However it shows that a safety margin always is a good thing,
both in the digital and analogue world.
 
>>The issue about electromagnetical wave reflections on audio cables
>due to lacking impedance fitting is High-End Voodoo, self-induced
>("induced", ha ha ha!) imagination, at least with normal cable
>lengths (and even if it does strike it�s still less audible than
>pre-ringing), but 96KHz is not.
>
>How about a rewrite that makes a little more sense?
>
Maybe you do, or some else native English speaker. If someone wants to
write an article or correct something, you can, and I�ll give you big
credits. 

>>I don�t have any references handy now because as I
>> stroll thru life I don�t always have in mind that I might need to
>> legitimate my opinions to people like you.
>
>The place to keep your references would be your web pages, no Mr.
>Grasso?
>
The place is in my head. And my site is 15 month old while I�m
somewhat older.

-------http://grassomusic.de-------
grasso at telebel.de