[vdr] Low volume on Pro7 ?

Harald Milz hm at seneca.muc.de
Sat Jun 11 15:47:33 CEST 2005


Rainer Zocholl <UseNet-Posting-Nospam-74308- at zocki.toppoint.de> wrote:
> Or -better- to insert a dynamic volume control (AVL audio/automatic 
> volume limiter) because very few people will like to have 140dB(A) comimg 
> from the TV... (if minimum environmetal "base" noise is assumed to be 40dB(A)),

<offtopic>

Hehe, I'd like to see a TV set that is _capable_ of delivering 140 dB (at
1m or so). The loudest bands in the 70s (Deep Purple and Grateful Dead) had
like 120 dB on stage, with umpteen 100W guitar amps running in parallel.
The surviving Deads are nearly deaf today. As for Ritchie, I don't know.
Today, the musicians are smarter, and use in-ear monitors or dampeners. 

> What's the sense of 100dB dyn. range?

Well why are soundcard makers advertising 24/96 or even 24/192? Same thing
I guess. 

> 2. Marketing, you have to buy better Amplifiers (I assume 4000W RMS 
>    output would be sufficient)

Depending on the loudspeaker efficiency. Let's assume an average
speaker for home use that delivers about 85 dB @ 1W @ 1m. To get 140
dB from this loudspeaker (within the microsecond before it turns into
a cloud of grey smoke), you would have to feed it 10^((140-85)/10) W ~
316 kW. A loudspeaker delivering 140 dB from 4.4kW would have to have
an efficiency of 140 dB - 10*log 4400 ~ 103 dB @ 1W @ 1m, which is
in the range of the best performing instrument speakers (Electro Voice
or Celestion). Their power handling is more in the 100..200W range at
more than 5-10% distortion, so you would want to have an array of at
least 40 of them, powered by 44 100 W Marshall or Boogie heads - in the
living room - well ... I do have an old Acoustic G100T guitar amplifier
(100W tubes feeding an EVM 12L speaker) in my living room, and if I
turned it up half-way I would be arrested by the police within 5 minutes
(especially considering my guitar playing skills but this is a different
story).

You get the idea... ;-) 

Alas, the point is not the high amplifier power. The dynamic
range is defined as 10 * log (highest level at a certain distortion
level / lowest level above the inherent noise of the all
circuitries together) (http://en.wikipedia.org/wiki/Dynamic_range,
http://www.absoluteastronomy.com/encyclopedia/s/si/signal-to-noise_ratio.htm).
For average room level music, 100 mW is enough (75 dB for the above
example speaker @ 1m), 1W is plenty, 10W wakes up your neighbour and
affects your hearing, and 100W starts to hurt. 4000W allows you to
run rock concerts in mid-size halls for a couple of hundred people,
and requires a 10 kW 3-phase feed which you don't usually have at home.

So for all practical purposes, we're talking about a usable range of
10W and below. Very few analog power amplifiers have a residual noise
in the µW range, so ... it's all very theoretical. No hi-fi op amp I
know of has a usable dynamic range of 140 dB (but I didn't check the
data sheets lately), and the PCB layout for such a circuitry is not far
from rocket science. 

> We already had this disussion with "CD" and the "giant" 90dB 
> they claimed to give.

Which is perfectly fine for most non-pro listeners. Well, back then the
record companies were about as flexible as they are today, and would rather
have kept selling vinyl LPs with their max. 65 dB dynamic range. 

> But you will hardly find any popular music which has not a reduced
> dynamic range. If it is 65dB it'll be good and better for your ears
> and equipment.

Most pop music has been mixed and compressed at far less dynamic
range. In many cases they are in the 30 dB ballpark, to keep things
loud enough when listening to car stereos or your average MP3 player
in a subway train. And radio stations tend to use additional limiters
before the power stages... 

But we're talking about AC3 audio, anyway, which is a different
thing... 24 bits * 6 db/bit sounds too good, doesn't it...  IMHO 24
bits are fine for the recording and mixing stage to keep rounding errors
and quantization noises low but for listening, 16 bits is fine, for all
practical purposes.

(And while we're at it, most teenagers who go to the disco frequently
do not have an actual dynamic range of 140 dB any more when they turn
20, especially not above 5 or 6 kHz. For them, the standard 44.1 kHz CD
sample rate is an overkill, and for the kind of music they often listen
to, 16 bits is overkill as well, which is why very many people can't
tell the difference between a clean CD recording and its 128 kbit/s MP3
equivalent ... ).

So yes, it's marketing to a "certain" extent. 

</offtopic>

Back to VDR - I suspect there's no easy way to volume adjust the AC3
stream coming from Pro7 and others -- sh*t, this would require decoding
AC3 which isn't allowed without a Dolby (R) license, right? BTW ZDF does
not have this low volume problem compared to other (non-AC3) channels,
only Pro7. But then, ZDF broadcasts less explosions than Pro7, and this
is unlikely to change if the Springer publishers (Bild-Zeitung) actually
take over Pro7/Sat1.

-- 
"You've got to think about tomorrow!"

"TOMORROW!  I haven't even prepared for *_________yesterday* yet!"



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