Frequency response question for Harvey Gerst or other audio engineering expert

[Kelly Dueck]

Harvey,

I just had the opportunity to record a string quartet with a pair of KM183's and a True Systems Precision 8 Pre-amp

This pre-amp has a published frequency reponse of 1.5 Hz to 500 KHz and sounds unbelievable. Totally open and airy.

My question is why does this incredible frequency response even matter given that the KM183's only have a frequency response of 20-20? How does all that upper frequency resolution even make it to tape? What's more, how does it even influence the sound coming out of a good pair of near-field monitors which might only have a frequency response of 35 Hz to 20 K? Do mics and speakers really record or transmit a much greater range of frequencies, only more weakly?

What's going on here, exactly?

Respectfully,

Kelly Dueck

 

[Harvey Gerst]

Take another look at the KM183 frequency response curve. It's flat down to 20 Hz, and probably good for an octave or so below that. At the top end, it's only 1 dB down at 20 kHz, and probably still usable to 25 kHz or beyond.

The other reasons why some preamps are flat well beyond the audible limits are increased clarity in the critical areas, and less possibility of artifacts showing up due to protective roll offs. The RNC is flat to almost 200 kHz, for example. It's a design philosophy which several manufacturers adhere to, among them, Rupert Neve.

Your recordings should have sounded stellar.

 

[Kelly Dueck]

Thanks for the info, Harvey. I always suspected something like that was the case.

Unfortunately the gear doesn't belong to me I had to coax it gently, but persistently, from the icy grip of a friend of mine who owns a commercial studio here.

It's amazing what you can get people to do once you grease them up with enough quality ale

The problem is now I'm spoiled for this kind of gear. It's quite a jump up from my MXL 603s's and Soundcraft Spirit M8 mixer!

 

[JerryD]

OK. Sure.

I'm not a engineering expert, but I did stay at a Holiday Inn express last night.

I agree with Harvey that it is flat down to 20 Hz.
Should sound stellar.

 

[electricbeats]

Hi Kelly and everyone !

check out following links:

http://www.cco.caltech.edu/~boyk/ARTICLES.HTM
"There's Life Above 20 Kilohertz:
A Survey of Musical-Instrument Spectra to 102.4 kHz" (" Includes short
description of others' work on perception of air- and bone-conducted
ultrasound, and points out that even if ultrasound be taken as having no
effect on perception of live sound, yet its presence may still pose a
problem to the audio equipment designer and recording engineer.")
http://www.cco.caltech.edu/~boyk/spectra/spectra.htm


"Oohashi and his colleagues recorded gamelan to a bandwidth of 60 kHz,
and played back the recording to listeners through a speaker system with
an extra tweeter for the range above 26 kHz. This tweeter was driven by
its own amplifier, and the 26 kHz electronic crossover before the
amplifier used steep filters. The experimenters found that the
listeners' EEGs and their subjective ratings of the sound quality were
affected by whether this "ultra-tweeter" was on or off, even though the
listeners explicitly denied that the reproduced sound was affected by
the ultra-tweeter, and also denied, when presented with the ultrasonics
alone, that any sound at all was being played."

greetings

klaus

 

[The Axis]

A "typical" human ear can only hear up to about 20 kHz. Some people can actually hear a little above that.
When people say that you can't hear frequencies above about 22 kHz, they are right, you can't. For most of us it is more like 18 kHz !
So if we can't hear it, why does it sound different with extended frequency response ?

Frequency response simply doesn't tell the whole story. The frequency response (steady tone) of a microphone or instrument also affects its TRANSIENT response (shape of waveform during changes in volume and recovery from them).

Since MUSIC is inherently changing volume and frequency constantly, the transient response of the instruments (mikes, preamps) above the audible range actually affects the shape of the waveforms that are within the audible range. So it actually does sound different and you can hear it. There is no subliminal magic or extrasensory prerception about it.

There is one good article about this called "The world beyond 20 kHz" at www.earthwks.com

Peace,
Rick

 

[Kelly Holdridge]

Hey, Axis, the link Earthworks supplies is actually to http://www.prostudio.com/studiosound/jan99/tech.html, but it came up as a dead link for me. Maybe it's accessible later on.

Dunno. I do think that upper harmonics (as described in electricbeats' second paragraph) can be detected with human ears, but for much the same reasoning that 44.1 kHz isn't adequate to fulfill 20 kHz sampling. Ooops, that's what Axis is saying.

Drool tastes good.