[Vintage-Audio] Re Frequency Behavior
bob
[email protected]
Tue Jan 13 20:08:00 2004
I didn't pay much attention to this thread until today. Man what a bunch
of missinformation. I don't even know where to start.
Hearing is a highly processed sense. Not only is the ear itself a highly
developed processor, but a goodly portion of the brain further processes
the data. Much of the confusion here is involved with the brain and its
processing.
In the pure physical transmission of sound, the audio frequency range
from 20 to 20kHz travels with about the same efficiency in free space
(free air..there is no sound in space). In the real world, the higher
frequencies bounce off of things and get absorbed in things and tend to
get time delays and losses that the low frequencies don't get. But in
general, they all get there about the same.
In hearing there are two effects that come into major play. The first is
that the preceived frequency response is a function of sound level (the
famous Fletcher Munson curves). For very low level audio, the human
hears only a narrow band centered around the voice frequencies. This is
not trained or learned but is in the very nature of the construction of
the ear and the firmware in the brain. You can demonstrate the
processing power of the ear-brain by recording a conversation you are
having in a crowded room, a noisy party. You have no trouble listening
to those that are talking to you and understanding what they are saying.
Take the recording into the quiet of you expensive sound room and play
the tape. You won't hear anything but the crowd noise. Your brain is
using visual (sorry Duanne), directional, tonal and other cues to
decipher the speech. This is the mechanism that allows a mother to hear
her child crying 10 miles away. This is why if you rip a concert from
the audience on your pocket DTR you end up with garbage. You can hear
the concert well, but the mic's don't have 20 lbs of processor working
the problem.
The second effect of interest is masking. The brain has a strange
ability to not hear some things. You won't hear a quiet tinkle in the
presence of a crash. You can see it on the scope, well in the loudness
range where it should be heard, but you cant hear it. The brain will
ignore stuff on nearby frequencies to large sounds. Effect is really
wierd, but is the mainstay of much of the perceptual coding that is used
on MP3, MD and video sound CODECs. they hide much of the digital crap
under big sounds where you cant hear them.
The concept of understanding speech is a very well studied field. The
exact bandwidth and shaping that provides the best comprehension of the
spoken word hidden in noise is manifest in our modern communication
receivers. Hide the spoken work in something other than noise (like a
cocktail party), and it is another issue. No electronic gadget can keep
up with the brain in pulling intellegence out of a cocktail party, in
spite of the liquid refreshments.
The female voice is not more comprehendable just more shrill and
grating. High frequcnies take less energy to create the same sound
level so for the same amount of energy, the higher frequencies are
louder. You are juse moving less air at the higher frequencies.. In you
100 watt amplifier, 90 watts are of use below 200 Hz and the other 10
watts take care of the rest of the spectrum.
WBob
Duane Fischer, W8DBF wrote:
>Sheldon,
>
>Yes, on all points.
>
>Pete was having some fun throwing math equations around, but Pete, I have a
>minor in mathematics from the University of Michigan, so be careful! You might
>have to buy some new batteries for your calculator OM! (chuckle)
>
>Because I am blind, I know far more about what people hear, listen to, filter
>out and so forth than anyone who is sighted. I use it every single day. A
>sighted person learns 92% of everything visually. That means all of the other
>senses, and there are far more than the five people think of, only 8% get used.
>What is the greatest sense organ anyhow? The skin! What do we do? We cover most
>of it up so its functionality is severely limited. Before we go down the path of
>nudists ... Ha Ha.
>
>Bob? If you want to debate hearing, write me off list. Who was it that said:
>"Everybody is talking, but nobody is saying anything?"
>
>DBF
>
>
>
>
>----------
>From: Sheldon Daitch <[email protected]>
>To: [email protected]
>Subject: Re: [Vintage-Audio] Re Frequency Behavior
>Date: Tuesday, January 13, 2004 8:39 AM
>
>Duane,
>
>I think we may be in total agreement. Maybe I wasn't quite as elegant in
>writing. The only part where I might disagree, in regards to radio
>reception, is under the situation where next channel interference is
>high enough, and the receiver has variable bandwidth filtering, so
>that the higher audio frequencies are filtered out. Depending on the
>depth and shape of the filters, one could strip out most of the higher
>audio frequencies, of a high pitched female announcer, and yet
>still pass the lower frequencies of a heavy-bass announcer. Under
>this unique set of circumstances, you could make a case for
>the lower audio frequencies.
>
>Pete has a nice explanation of the speed of sound, but I think what he
>overlooked is the attenuation factor of higher audio frequencies
>vs lower audio frequencies. I believe that was part of your concern,
>wasn't it, range, not velocity.
>
>Sheldon
>
>"Duane Fischer, W8DBF" wrote:
>
>
>
>>Sheldon,
>>
>>First, the human ear is trained from before an infant is born to listen in a
>>specific frequency range for vocal patterns. Hence, humans focus on certain
>>frequency ranges and filter out others without even realizing they are doing
>>
>>
>so.
>
>
>>A higher pitched voice tends to be heard above the general din of noise
>>pollution we all experience in our daily comings and goings.
>>
>>The best example of this filtering I can think of, is that of a mother hearing
>>her child several rooms away with a TV set going, people talking and all sorts
>>of other racket. She hears the child whimpering and nobody else in the room
>>hears a thing.
>>
>>The low note carries the greater distance because it has a longer wavelength.
>>For instance, the kid down the street with the kickers in his trunk. You can
>>hear the bass a quarter mile away, but nothing else.
>>
>>It was said that a female announcer on a radio station could be heard at a
>>greater distance because of her high pitched voice. I disagreed. The radio
>>signal carries only so far, regardless of what sex is doing the talking.
>>However, because her voice is generally of a higher pitch it may be easier to
>>hear because it is above the area of the general noise. So it 'appears that
>>
>>
>she
>
>
>>is heard farther away simply because the frequency of her voice is higher than
>>the background noise.
>>
>>Your thoughts?
>>
>>DBF
>>
>>----------
>>From: Sheldon Daitch <[email protected]>
>>To: [email protected]
>>Subject: Re: [Vintage-Audio] Re Frequency Behavior
>>Date: Monday, January 12, 2004 3:42 PM
>>
>>Duane,
>>
>>Maybe we are trying to compare apples and oranges here.
>>
>>In general, lower audio frequencies are attenuated less than
>>higher frequencies, thus, you can hear the rumble of the loud
>>bass much further away than the higher frequencies from the
>>same boom box.
>>
>>When you get into the second part of your question, which
>>announcer would be "heard" at a greater distance, assuming
>>no interference, one would think there should be no
>>difference in radio range, if that is the intent of your question.
>>
>>Now let's subject the signals to some interference, and
>>then it becomes a little more difficult to answer, as the filtering
>>necessary to reduce or eliminate the interference might also
>>be the same frequency range as the announcers voice.
>>
>>So now, at the RF side of the equation, I am at a loss for
>>a definitive answer, as I think it might be a lot more
>>subjective and related to the skills of the listener.
>>
>>More thoughts?
>>
>>Sheldon
>>
>>"Duane Fischer, W8DBF" wrote:
>>
>>
>>
>>>Is it true that a higher note is often easier to hear, but a lower note
>>>
>>>
>>travels
>>
>>
>>>a greater distance?
>>>
>>>Now leaving the length of the sound wave out of the discussion momentarily,
>>>given a male and a female announcer for a radio station, speaking at the
>>>
>>>
>same
>
>
>>>volume into the same mike, which signal will be heard at the greatest
>>>
>>>
>>distance?
>>
>>
>>>The one with the highest voice pitch or the one with the longest wave
>>>
>>>
>length?
>
>
>>>Duane W8DBF
>>>
>>>
>
>