R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 [3]  All   Go Down

Author Topic: frequency response vs. impulse  (Read 10060 times)

compasspnt

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16266
Re: frequency response vs. impulse
« Reply #30 on: September 30, 2005, 02:54:07 PM »

Eric, I think that Max is now talking about the sound of older/vintage/tube/ribbon mics through vintage/tube/pre's/consoles v. modern/fet/what-have-you ones, BEFORE even going to a recording medium.  I think he is stating that the earlier systems have a more rounded, full-bodied tone, and the newer have a more strident, harsh tone which begins to show up at 2k.  This is leaving out the tape v. dig debate entirely.

Some of us discussed this at little bit on my guest moderator Forum back in Feb-March.  I agree that there is a difference, but to what to ascribe this difference I am not totally sure.
Logged

Paul Frindle

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 380
Re: frequency response vs. impulse
« Reply #31 on: September 30, 2005, 04:50:40 PM »

[quote title=Eric Bridenbaker wrote on Fri, 30 September 2005 02:00][quote title=Paul Frindle wrote on Thu, 29 September 2005 20:26]
Timeline wrote on Thu, 29 September 2005 19:40

A crash symbol can be measured to 27khz.

Hey Paul,

This is definitely something think about, it all makes sense! Hadn't considered any of this.

Question: If captured ultrasonics are subject to double intermodulation upon playback, would the same process also apply to captured frequencies under 20KHz?

In other words, are we hearing this double IM effect anyways, even in a recording that is bandlimited 20Hz-20KHz? Wouldn't for instance 10KHz also be subject to the same rules as 25Khz?

Does it make sense that intermodulation in a non-linear system will occur for all frequencies, whether in the audible range or ultrasonic?

Still trying to get a deeper understanding. Hopefully I'm wording this OK...

Best Regards,
Eric


Yes very definitely. Intermod products will appear for signals within our hearing range if loud enough, both in the air and in the ear itself - although normally we tend to be unaware of the ear's problems IME, unless specific tests are done that make us concentrate on them.

The point would be that for the situation I described above the intermodulation caused by the air is really at the initial boundary between the instrument and the air because the sound pressure level drops dramatically with distance. So if you are listening from a meter or two away you are hearing mostly just one level of intermodulation. SO the subharmonic beating of supersonic HF you describe would occur mostly from this initial boundary.

But if you put a mic in front of the instrument and pass this at full supersonic bandwidth out of a speaker at similar levels you will have two such boundaries, the original instrument to air and the speaker to air as well. And this is assuming that both mic and speaker are hypothetically perfect.

BTW on another point - I can find no evidence that the ear itself is capable of creating subharmonics from supersonic HF. Once the signal gets beyond our hearing range it has truly gone as far as I can tell in tests I have done. This was something I didn't expect at all since beforehand I assumed that the mechanical bits of the ear would at least have some sensitivity to the HF and some non-linearity! But it seems not to be so for some reason.

The tests I did were of course inspired because our company was involved in designing high bandwidth reproduction systems - and there was a fair degree of pressure to find 'something' that improved with higher B/W. Sadly to date I have found none - if the most faithful reproduction of the original sound is what you are after Sad
Logged

Eric Bridenbaker

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 342
Re: frequency response vs. impulse
« Reply #32 on: September 30, 2005, 06:08:50 PM »

compasspnt wrote on Fri, 30 September 2005 14:54

Eric, I think that Max is now talking about the sound of older/vintage/tube/ribbon mics through vintage/tube/pre's/consoles v. modern/fet/what-have-you ones, BEFORE even going to a recording medium.  I think he is stating that the earlier systems have a more rounded, full-bodied tone, and the newer have a more strident, harsh tone which begins to show up at 2k.  This is leaving out the tape v. dig debate entirely.

Some of us discussed this at little bit on my guest moderator Forum back in Feb-March.  I agree that there is a difference, but to what to ascribe this difference I am not totally sure.

Thanks Terry,

I'd love to check out that thread, do you remember what it was called?

I don't have any experience with tube consoles, but I can say that in guitar and bass amp world, tubes mean everything to me.

For a main tone, I'd always pick the tube amp over the solid state... this is very important for the distorted guitar, but even clean sounds for guitar and bass guitar seem well, flat and kind of lifeless without the tubes. There's just so much more complexity and nuance to the tube sound, lots to play with.

Sure solid state distortion is OK for an effect or a novelty sound in a track, also throwing a pedal in front of the tubes is good for getting color, but to use strictly solid state distortion for the main tone... can't do it, it seems too fatiguing. Some bassists like to run a Bryston or Hafler for their rig, and it does have a lot of clean bottom end, but in the tones I've liked there's usually a tube pre or compressor involved somewhere. I am starting to like these new digital amp simulation units like the line six pod, plugins like amplitube and guitar rig, which I would definitely pick over solid state amps. The programmers have somehow managed to squeeze a lot of tube like complexity out of them... it can be scary.

Cheers,
Eric
Logged

compasspnt

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16266
Re: frequency response vs. impulse
« Reply #33 on: September 30, 2005, 07:00:01 PM »

Eric Bridenbaker wrote on Fri, 30 September 2005 18:08



I'd love to check out that thread, do you remember what it was called?


There was a lot I unfortunately don't have time to read back through, but perhaps

http://recforums.prosoundweb.com/index.php/t/3761/6490/?SQ=7 5f1672793e04fb86755b9058d22ae73

Or maybe a bit in

http://recforums.prosoundweb.com/index.php/t/3884/6490/?SQ=8 9251d338434ef3878fc03c429e40dda


Quote:

I am starting to like these new digital amp simulation units like the line six pod, plugins like amplitube and guitar rig, which I would definitely pick over solid state amps. The programmers have somehow managed to squeeze a lot of tube like complexity out of them... it can be scary.




Yes, the L6 pods "make me very scary..."  to quote the inimitable Sol Rosenberg.
Logged

Eric Bridenbaker

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 342
Re: frequency response vs. impulse
« Reply #34 on: October 01, 2005, 11:50:07 AM »

Paul Frindle wrote on Fri, 30 September 2005 16:50

Eric Bridenbaker wrote on Fri, 30 September 2005 02:00



Does it make sense that intermodulation in a non-linear system will occur for all frequencies, whether in the audible range or ultrasonic?

Best Regards,
Eric


Yes very definitely. Intermod products will appear for signals within our hearing range if loud enough, both in the air and in the ear itself - although normally we tend to be unaware of the ear's problems IME, unless specific tests are done that make us concentrate on them.

The point would be that for the situation I described above the intermodulation caused by the air is really at the initial boundary between the instrument and the air because the sound pressure level drops dramatically with distance. So if you are listening from a meter or two away you are hearing mostly just one level of intermodulation. SO the subharmonic beating of supersonic HF you describe would occur mostly from this initial boundary.

But if you put a mic in front of the instrument and pass this at full supersonic bandwidth out of a speaker at similar levels you will have two such boundaries, the original instrument to air and the speaker to air as well. And this is assuming that both mic and speaker are hypothetically perfect.

BTW on another point - I can find no evidence that the ear itself is capable of creating subharmonics from supersonic HF. Once the signal gets beyond our hearing range it has truly gone as far as I can tell in tests I have done. This was something I didn't expect at all since beforehand I assumed that the mechanical bits of the ear would at least have some sensitivity to the HF and some non-linearity! But it seems not to be so for some reason.

The tests I did were of course inspired because our company was involved in designing high bandwidth reproduction systems - and there was a fair degree of pressure to find 'something' that improved with higher B/W. Sadly to date I have found none - if the most faithful reproduction of the original sound is what you are after Sad


Thanks Paul,

It seems to be the case that any obvious benefits of extended HF reproduction would occur from effects produced in the known audible range.

I'm unsure about the specifics behind the Audio Spotlight, but the Wroclaw University of Technology study (the one K.K posted) used 100dB SPL ultrasonics, with tones at 39/40Khz and 159/160 Khz to produce an audible 1K differential tone. The paper clearly shows how the ultrasonic frequency used and sound pressure dropoff with distance are important considerations to producing the effect.

From the 100dB SPL source, they were able to produce a 1K differential wave of 53dB SPL a few cm from the source, it dropped to around 50dB at 1 meter, then very quickly receded at distances beyond 1 meter.

It's clear that non-linear modulation of soundwaves can occur at a low amplitude, relative to the source, and it can be weak enough to the point were many have considered the effect unimportant.

However, this aspect may not necessarily suffice as a case for absolute negligibility of these effects. Consider relative amplitudes that occur in the case of dither applications. Many audio engineers would agree that it improves the sound, though the dither noise is at a level only sufficient to mask error that is many dB below the signal it's being added to.

Thanks Again,
Eric

Logged

Paul Frindle

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 380
Re: frequency response vs. impulse
« Reply #35 on: October 01, 2005, 07:12:27 PM »

Eric Bridenbaker wrote on Sat, 01 October 2005 16:50

[Thanks Paul,

It seems to be the case that any obvious benefits of extended HF reproduction would occur from effects produced in the known audible range.

I'm unsure about the specifics behind the Audio Spotlight, but the Wroclaw University of Technology study (the one K.K posted) used 100dB SPL ultrasonics, with tones at 39/40Khz and 159/160 Khz to produce an audible 1K differential tone. The paper clearly shows how the ultrasonic frequency used and sound pressure dropoff with distance are important considerations to producing the effect.

From the 100dB SPL source, they were able to produce a 1K differential wave of 53dB SPL a few cm from the source, it dropped to around 50dB at 1 meter, then very quickly receded at distances beyond 1 meter.

It's clear that non-linear modulation of soundwaves can occur at a low amplitude, relative to the source, and it can be weak enough to the point were many have considered the effect unimportant.

However, this aspect may not necessarily suffice as a case for absolute negligibility of these effects. Consider relative amplitudes that occur in the case of dither applications. Many audio engineers would agree that it improves the sound, though the dither noise is at a level only sufficient to mask error that is many dB below the signal it's being added to.

Thanks Again,
Eric




Yes this is a good point - the non-linearity in air does drop off quickly but it is never completely absent.

The point of the illustration is that two (or even 3) lots of significant intermod will always produce more artefacts than what you would have heard in the real live performance wrt the distance you are from the sound source.

I think it's a problem that is practically unresolvable? I can't think of a solution myself, but I am open to any suggestions?

The thing then is, having established that the 'true' subharmonics caused by supersonic sounds from the instrument exist in the recording environment within our range of hearing - why are we trying to send freqs that are above our hearing range at all? We cannot make a good argument for it on the basis of reproduction fidelity (in the air we actually listen to), neither can we make an argument for it on the basis of what we can actually hear.
All the (very understandable) misconceptions about squarewave responses and the like can be wholy discounted on the basis of the laws of physics and math - however much marketing people may feel 'pictures' of squarewaves might advance their cause. We may like the sound of such things subjectively under some conditions (particularly where signal clipping occurs) - but the artefacts are not a reflection of greater accuracy of reproduction as far as we humans are concerned, in fact there is quite a bit of evidence that they are most likely detrimental (the above situation being just one simple example that no one could dispute). Therefore we should at least be honest enough about it to hessitate in applying such thinking to reproduction systems in a blanket swoop Smile

I of course remain completely open minded and if I ever come across a defensible reason for higher reproduction freqs I will be the first to say so. It would be very much easier if I COULD find something as this is what everyone would greatly prefer - not least of all those that have already sold it to people Smile
Logged

timrob

  • Full Member
  • ***
  • Offline Offline
  • Posts: 131
Re: frequency response vs. impulse
« Reply #36 on: October 01, 2005, 11:42:31 PM »

Paul, Thanks for that. I don't thin it could have been expressed more eloquently.

Cheers
Logged
Tim Roberts
Waterknot Music
Nashville


---------------------------
Ours is not to understand.
Ours is just to record the band.
-Unknown

Tomas Danko

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 4733
Re: frequency response vs. impulse
« Reply #37 on: October 02, 2005, 01:29:41 PM »

ESP hearing used to be very expensive, only available to the real pro musicians. But thanks to the cheap assembly lines in Indonesia these days, todays kids can now experience this. It's called LTD hearing.


I'm not as young these days, so I'd say I only have got LTD hearing.


The other day I met a customer with huge elephant-like ears. He told me he never forget a sound.
Logged
http://www.danko.se/site-design/dankologo4s.gif
"T(Z)= (n1+n2*Z^-1+n2*Z^-2)/(1+d1*z^-1+d2*z^-2)" - Mr. Dan Lavry
"Shaw baa laa raaw, sidle' yaa doot in dee splaa" . Mr Shooby Taylor
Pages: 1 2 [3]  All   Go Up
 

Site Hosted By Ashdown Technologies, Inc.

Page created in 0.03 seconds with 19 queries.