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Downward Dynamic Range - a fuller description.

Info regarding Downward Dynamic Range (DDR) was first published back in 1995 as part of "Chapter 1, Philosophy" of my "TubePreamp CookBook", where the section on DDR starts on Page 12.

It's a 56kB PDF file but I don't seem to be able to upload it. If anyone's interested in the full chapter, I can email it to them, or maybe someone can help me upload it...?

But below is just the DDR part in text format, hope this better explains what I consider to be a key aspect of hifi reproduction.

And the KEY phrase in it all is:

"... but the room sound would have been there all the time, every “clack” able to be heard dying away naturally to zero, even through the new sound energy she was putting into the space with each new step"

Regards, Allen
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Axiom #9—Realism requires Real World Dynamic Range!

Dynamic range as conventionally defined is not so hard to obtain. CD gives you a ~95 dB ‘dynamic’ range if you measure from the noise floor to peak level, but that’s got nothing to do with what we hear in life. Here the Guru offers a new concept :

“Downward Dynamic Range”. (DDR)

This is what allows us to hear low level sounds while louder ones are playing. This is where ambient cues come from, where ‘room sound’ is found and where every digital system I’ve ever heard just doesn’t cut it!

I have a friend, Robert Parker, who’s always loved digital, and for his purposes as a specialist recording engineer it may be just what he needs. To try and convert me to it’s joys, he once brought over a master tape he’d made of a operatic soprano, singing with solo piano accompaniment, recorded in a large live studio.

I was of course curious and we played it via the actual machine he’d recorded it on—a SONY 1620 or whatever—straight into my reference system—all tube, NFB free and electrostatics…

He’d started recording just before the singer arrived, and although it seemed totally silent, when you turned the playback way up—Wow, you could hear the street noises outside—and when she opened the door to come in, this traffic became way louder. And throughout all this –80dB stuff, there was no background electronic noise!

So far so good, and he was starting to enjoy himself—he was really putting it to the Digital Disapprover!

And so far it was quite impressive, and it wasn’t till she started to walk across the studio towards the mic’s that I got what was wrong.

The room was totally quiet again with the door closed and the gain returned to a normal level, actually it was strangely dead, but the floor was hard and you could really hear that characteristic sound of her high heels:

“Clack”—“Clack”—“Clack”.

With each heel strike the room was illuminated acoustically so you could now ‘see/feel the space’ but instead of fading away, the space ‘vanished’. It was like you were in a completely dark room and hitting a camera strobelight each time she stepped:

“Clack”—Flash! “Clack”—Flash! “Clack”—Flash!

But just as there’s no light once a flash is gone, there was no echo, no reverb—once the heel sound itself was over—it just switched off with none of the natural decay you would have heard had you been there.

Totally artificial, and totally unreal!

OK, if he’d been recording with an analog recorder, sure there would have been some hiss, and her actual heel strike may have been a little less accurate, but the room sound would have been there all the time, every “clack” able to be heard dying away naturally to zero, even through the new sound energy she was putting into the space with each new step.

The ability to accurately reproduce low level information in the presence of other stronger signals is one of, if not the most vital property of really good audio gear!

And as I said before, we use the term Downward Dynamic Range to label this parameter but perhaps it would be better named “Effective Dynamic Range” or even “How far down can you hear all at once Dynamic Range”.

It’s what I listen for when adjusting running current on output tubes; setting loading resistors for cartridges; choosing capacitors, resistors, tubes, wire; adjusting anti–skating on tone arms. In fact in everything you use a listening test for—DDR is a key factor, even if you didn’t have a name for it before.

It’s musical life, it’s the difference between analog vinyl and CD, between a ss preamp and a good tube one, and the difference between the original Quad ESL and the ‘63.

It’s the difference between a singer direct and through even the best PA system, it’s the opposite of compression, and of multi-way speakers with complex cross–over’s.

It’s the difference between sound and music, between canned and real!

To really achieve our stated purpose of reproducing music and other aesthetically rewarding sonic events, we need to maximise the total amount of information we can record and then reproduce all at the same time in the listening environment, while minimising any distortions, additive or subtractive!

If we take our ideal bandwidth requirement of 7 decades and plot that on a graph against the simultaneous DDR requirements of ~100dB that exist and you can hear at an acoustic concert in a very good hall, we end up with a pretty extreme picture.
__

Here you can see why audio is such an amazingly challenging and sensitive arena to work in, and why it is of much broader and extreme scale than any other category of electronics.

Once you put a system together that has great DDR, and you enhance the definition and clarity with some real bandwidth, you’ll start getting closer to our objective, and then some pretty strange metaphysical things can start happening.

You’re starting to manifest the original performance in your own perceptive field, and if your set-up is not quite right, the ‘sound’ will still be great, but as it will not exactly overlay the "Metaspace" of the original performance, the music will feel somehow weird—wrong!

For example, at this level, on a live recording, if the system’s out of absolute phase, or if the channels are reversed left to right, it may still sound fantastic but there will be an over–riding feeling of: ‘Something’s kinda weird round here’,

And as this particular weirdness only occurs when you’re really really close to perfection—don’t become discouraged and tear it all down—it’s a positive sign and you’re now down to fine adjustments, subtle changes—take your time but keep progressing—for you’re close to achieving something very special…

“And how will I know when I’ve achieved it?”

I’ll assume the Zen position and suggest:

“You will know true enlightenment only when it happens, but then you will know!”.
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  Michael Percy Audio  


Topic - Downward Dynamic Range - a fuller description. - Allen Wright 10:52:37 09/06/07 (7)

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