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You seem to be recommending random measurement of "things" ...

157.128.218.206

In Reply to: RE: Not necessarily, IMO - we may (currently) have no idea what it is we need to measure! :-)) ... posted by dromney on February 14, 2011 at 16:01:36

without knowing what "things" you should be measuring?? :-))

And as far as making one amp sound like another - the designer whose ss amps I use started out by deliberately injecting some H2, to make them sound a bit "tubey-like". (He's now moved away from that "trick"!! :-)) )

So it is easy to play with the relative magnitudes of successive even and odd harmonics, to change the sound of an amp.

As an engineer, please tell me what artefact one should measure, to define how much the amp will project a singer forward.

Or ... agree with my proposition that, if we knew what to measure, to measure the amount of "forwardness", then we could predict how much an amp would project a singer's voice forward of the plane of a loudspeaker. But because we don't know what causes this, we have no idea what we should be measuring. :-))

Regards,

Andy

Regards,

Andy

Follow Ups:

RE: You seem to be recommending random measurement of "things" ... - dromney 12:40:07 02/15/11 (2)
Not sure why it sounded like I am proposing measuring random things. The signal when passed through an amp is altered. The alteration of the signal can be expressed in the frequency domain as a transfer function. The transfer function expresses the changes in the frequency domain as caused by all components. The expression would account for all capacitance and inductance as well as active components altering or adding frequency information (such as added harmonics or delays).

Now once the transfer function for each amp is understood it can be used to compare the two amps and what they are doing differently to the signal. After that point you can add, or subtract, delays/capacitance/inductance to make the functions more similar and while doing that you can determine the change that we would interpret as more forward sounding etc. Of course what all designers say is that their amps are "neutral", but if that were true they would all sound the same! Even the component layout and ground plain will make contributions.

When someone like Bob Carver is talking about tuning his amps to sound the way he likes them I am sure he knows when and what he wants to add or subtract to his amps to change the way they sound. A lot of that is by experience that only someone like he has. I have never read in a book how to do this, but I have watched other engineers do exactly the same kind of tuning on RF amps. Typically they have a spectrum analyzer in front of them and add or remove capacitance to certain portions of the circuit to bring down certain lobes in the frequency domain. If you ask them how they know where to do it, it is sometimes a "I just know from doing it for 25 years".

Anyway, I believe that it can be characterized and may be in engineering course work that I have never taken. Audio design is a niche career! The design may be art, but it can be described by science and measured and repeated.
- RE: You seem to be recommending random measurement of "things" ... - josh358 18:13:55 02/16/11 (0)
  "Black art." By virtue, mostly, of its not being in books. The point at which you rely on your own observations and discoveries, or those that were passed on to you personally.
- RE: You seem to be recommending random measurement of "things" ... - ahendler 13:18:27 02/15/11 (0)
  Of course the transfer function is being created using only what we can currently measure. To say that we know everything about sound and can measure everything that makes it up is the same as saying in the 1900's that we know everything there is to know about the world and there is no new science to be discovered and then along came quantum mechanics. I feel strongly as an electrical engineer that there is a lot about sound that we have not discovered yet how to measure
  Alan
RE: You seem to be recommending random measurement of "things" ... - josh358 16:28:12 02/14/11 (2)
Well one thing that will do it is increasing or decreasing the energy in the presence range. A boost in the freq response will bring the sound forward, a cut will push it back. Also, bass levels fall off at a distance.

I'm not saying that that's what happened in this case -- I'm generally puzzled by reports of the effect of electronics on imaging -- but I thought I'd mention it as a matter of interest. What makes a sound recede or come forward is actually pretty well understood: besides those changes in frequency response, perceived distance is a function of the nature and amount of reverberation. A recording engineer can make make a dry recording distant or close by changing the wet/dry mix, reverberation spectral balance, early reflection timing, and other factors in a digital delay. We do some of that ourselves using passive acoustic means, e.g., by moving speakers away from room boundaries and suppressing reflections so that reverberation is delayed by a minimum of 10 ms, which is the minimum required to impart a sense of spaciousness to the sound (in a digital delay as well as a listening room).
- Sure, Josh, understood ... - andyr 16:35:56 02/14/11 (1)
  but what do you suggest should have been measured for the two amps, to explain why one pushed the singer several feet forward then the other?
  
  I doubt that one was creating its own "reverb" while the other one wasn't. :-))
  
  Regards,
  
  Andy
  - RE: Sure, Josh, understood ... - josh358 16:46:01 02/14/11 (0)
    That's one of the great mysteries in audio for me! For example, why do tube amps image so well? They just do! I've read about a million explanations, but I have yet to read one that convinced me we really know.
    
    Lateral imaging is easier to explain, since if the two channels of the amp aren't precisely matched you'll get frequency or phase differences between the channels that could interfere with imaging specificity. Who knows, that might also have something to do with depth perception, since the two can interact.

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