GoodSoundClub - Romy the Cat's Audio Site - Contributing factors in compressed sound

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Topic: Contributing factors in compressed sound

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Posted by malinowski on 08-23-2007

I have been searching for a good discussion on this subject for a while an yet to come across anything that really explained this:
What are the causes/factors of compressed sound?
I know it when I hear it, and have heard this phenomenon attributed to everything from valves to drivers to enclosures and room treatments.. etc..
ROmy, you've mentioned that the quest for imaging is frequently accompanied by compression.. and you've also said how the TAD drivers (or sytems - unlear which) had a sound that was notably effected by compression.
What are the factors?
for the amplication stage? are certain driver tubes more susceptible to sounding compressed? is an el84 a driver known to image very well also more prone to this compressed sound? or is this the result voltages people choose to operate these by?
for the drivers? what drivers are characteristically more compressed sounding?
why would the TAD td-2001 driver sound more compressed than say.. a radian driver?
are compression drivers less prone to sounding this way than direct radiators?
a recent post about the RAL drivers mentioned a problem with compression.. is this true for all efficient cone drivers?
i was mulling over using something like the supravox 165-2000 for a midrange to go in my secondary.. less efficient system.. but don't want compressed sound...
i hate that whompy, poppy compression in my face.. it like being stuck in room with jim carrey or something.. what i want is music that feels like cool cucumbers on my eyes... and music that in so many aspect sounds like silence, that is present in my head.. not sticking its armit in my face.. anyhow.. thats how i characterize what i think is compressed sound. I am not very knowledgeable about these things.. i just know what i like and don't...
anyhow.. are there midrange direct radiators that are efficient and don't sound compressed?
what are the factors? at least from an amplfication stage and driver stage to avoiding this phenomena?

and why do you have a spellcheker when you intentinaly misspell everything... you should have a spell-wrecker.. that would be clever.
ok. thanks! best regards to all the readers here.. i appreciate you a lot.. even though i am usually reading and lurking here..

Posted by malinowski on 08-23-2007
fumbling thru my closet, found a shrunken sweater that just reminded me an analogy.. what shrinks the wool? I had this lovely loose mohair sweater that I mistakenly threw into a hot wash.. not its a dense ruined little rag... what factors do this to our music? at least those factors we can control from the reproduction side of things.

Posted by Romy the Cat on 08-24-2007

Well, it is a good subject and my reply probably will be lengthy. However, do not expect to read anything worthy in there as I have no answers.

We all know about the compression, the people with develop listening culture and more or less evolved listening intelligence can recognize compression, or more frequently the signature of the mechanisms that create compression (a loaded statement). We all know about the negative consequences of compression but do we always know the reasons and the mechanism why the compression took place? (Let disregard the situations when a compression applied intentionally)

BTW, Amphissa recently has pointed out an article at http://spectrum.ieee.org/aug07/5429 that related to the subject.

So, if we do not know where the compression comes from then let at list to identify the source of compression.

1) Recording process. This is a big avenue for compression. The recording equipment, the acoustics, the microphones, the microphoneing techniques and many other things could contribute to compression. I personally do not record and have no experience with subject, perhaps someone who does would be able to say anything rational about it.

2) The format. Different formats have own fundamental influence to compression. I am completely confused about it as I have witnessed in many instances when a format with less dynamic range subjectively sound less compressed then formats with objectively higher dynamic range. Perhaps the key is implementations?

3) The playback electronics. The lowering noises, increasing dynamic range and providing a sufficient extension of to peak-power over operational power do help. Still, there are zillion of other factors… How deep should we go into assessing the contribution to compression? Some people look at the shape of the electron cloud inside of tube and the space between the elements of the tube as a prediction of dynamic characteristics of the tubes. Then we have the operation point, loads, the power supplies, the components, the parasitic capacitance and inductances, the magnetics … etc… etc… etc.. Go figure…

4) The acoustic systems. The sensitivity of acoustic systems is defiantly the key but the highest sensitively number is not automatically brings higher absolute dynamic range. There are many factors in loudspeakers that are responsible for compression but the irony is that by intellectually take care of them would not be an assurance of better subjective dynamics. In this section I have some expertise and I would talk about it a lot but how worthy would it be? Beside there is always a mystery for me that here and there pop up some products that define all compression rules and being low sensitivity loudspeaker they play subjectively as then have no dynamic limitations (The Wilson Grand Slam and above for instance) so, go figure again…

5) The acoustic environment of playback. That is very important contributor to but it is not without “issue”. Overdumping increases subjective perception of compression ….

6) Electricity. A big contribution to compression. Recently I was informed that when a very peak of our voltage sinusoid is clipped then it is the key for compression as current is cared at the very last tip of the wave. The current distortions, current patterns and this contribution to sound are a separate subject. It is not well researched; at least I know little about it…

So, did I say anything useful about the nature of compression? I do not think so. I wish I know something useful then I would be able to employ it.

Rgs, Romy the Cat

Posted by malinowski on 08-24-2007

Thanks Romy,
I would have thanked you sooner but I had the day OFF of my day job today and had no time to post until now.
*cracking up*
I had a feeling there was no easy answer, wasn't sure if I was missing something, had scoured posts for a while and never saw one.
Anyhow, thanks.

"The sensitivity of acoustic systems is defiantly the key but the highest sensitively number is not automatically brings higher absolute dynamic range. There are many factors in loudspeakers that are responsible for compression but the irony is that by intellectually take care of them would not be an assurance of better subjective dynamics."

It would be interesting to tackle a piece of this topic at a time. In this case I was thinking about what effect the pitch, size(in relationship to freq.) and material of a membrane or cone might have on this "compression".
Two examples stand out in my mind, the ScanSpeak drivers you use for lower bass are oft noted for lacking "compressed sound" characteristic, also the TAD tl-1102 (94db 11" alnico) drivers have been said to exhibit this same quality. Duke LeJeune tested a lot of drivers looking for ones that had this quality and really liked these. Now, looking at them both (own a pair of each), I notice how they have some similarities... both have relatively (and unusually) flat cones (less coned? sorry i don't know the term for this geometry) and both pay careful attention to the quality and properties of their paper.
Which leads me to wonder if the pitch of the cone might be one contributing factor?.. most compression drivers are also relatively flat.
Hmmm... this is why i was curious about the supravox 165-2000 drivers.. they look like the tl-1102's and the Scan Speak 25W/8565-00.. the three combined in sealed enclosures and a raal ribbon might make and interesting experiment for a "monitor"
an even better experiment in context with this thread.. might be to create a variably pitched cone.. so see what extent this one area contributes to this phenomenon... any volunteers? lol
ok. thanks for your ear/s and input..

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