[LAU] Sampling rates [WAS]: Re: jack/oversampling

[Gene Heskett]

On Sunday 16 March 2014 20:19:50 Lorenzo Sutton did opine:

> On 16/03/14 19:39, Gene Heskett wrote:
> > On Sunday 16 March 2014 14:25:14 Ralf Mardorf did opine:
> >> On Sun, 2014-03-16 at 08:58 -0700, Len Ovens wrote:
> >>> I would mix the project  at 48k or 96k
> >> 
> >> Why 96 KHz? 48 KHz doesn't cause any issues, but already provides
> >> best sound quality.
> > 
> > That I think is a personal call Ralf, primarily because at 48 Khz,
> > your anti-aliasing filters had better be very very good brick walls
> > by the time you get above 24Khz in input content
> 
> Can anyone point out a commercially available microphone used in the
> audio recording domain which will actually pic frequencies above 20 kHz?
> 
An Altec M-21b, new in about 1955 or so, probably 40 years out of 
production now has usable response beyond 20Khz.  The PZM, a similar but 
electret powered condenser mike, new in about 1985 IIRC also goes up into 
that range.

> Likewise can anyone point out any commercially available speaker used in
> the audio reproduction domain which will actually reproduce frequencies
> above 20 kHz?

Is the Altec Lansing 075 ring radiator tweeter still available?  I once saw 
some scope photos of the output of an M-21b, 3' away & on axis of the sound 
output of the 075 driven by approximately a watt of a square wave at 25Khz.  
The square wave was still recognizable.  In the '50's we would set an 075 
in the center pocket of the Cobra Horn of a JBL Hartsfield speaker, a huge 
corner horn that was very good before we did that, and made it raise the 
hair on the back of your head real if your eyes were closed and a 30ips 
recording of the Dukes of Dixieland was playing from 10.5" reels on a 
Berlant-Concertone tape deck.  The only thing that gave it away was the 
tape hiss, a good 68db down.  There may yet be a few of those around, but 
very few since it sold new in the 1950's for $750.  That tweeter added 
another 100 to the price.

The Hartsfield was fairly efficient too, better than the Voice at the time.  
We could hit 130+db in the front room at Woodburn Sound Service in Iowa 
City Iowa, with a 10 watt rated Fisher amplifier driving it.  And I am 
talking 130 very painful db's.

> If the audio produced is made for fruition of humans it makes absolutely
> no sense to try and capture or reproduce anything above 20kHz, and for
> average individuals 15kHz would probably more than enough.
> 
> And in case anyone is tempted to state that even if we don't hear them
> frequencies above 20kHz influence the way we hear or 'perceive' music,
> please also attach any _scientific_ study/paper/evidence (e.g.
> large-scale blind tests etc. not anecdotal evidence) to such statement.

This is, according to your definition, anecdotal.  I spent 2 years Chiefing 
at a radio station in No. Kalipornia, who had one of those ultrasonic 
motion detector burglar alarms.  It wasn't working so the first thing I did 
was fix it, dead battery.  Then I had to rig it with a disabling switch to 
shut off the power amp that drove the piezo speakers in it.  I couldn't 
hear it as such, but my ears would feel like I had just walked into a high 
pressure chamber that yawning wouldn't fix, and in 5 minutes I had a 
splitting headache.  So it wound up with a switch that the owner could turn 
on when he left for the day.  To this day I can walk into a shop with one 
of those things and tell them if its running right, surprising many a shop 
owner who thought the installation was a secret even from his employees.

FWIW, they aren't worth it because of the false alarms they generate when 
the wind is blowing against those huge plate glass front windows which can 
move 1/2" or more in a good spring breeze.  Sets them off every time.  To 
the LE people, they are the little boy crying wolf and are ignored.

> Lorenzo.
> 
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Cheers, Gene
-- 
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