PHILIPS RED BOOK

[Don Hills]

I finally caught onto the concept, but isn't that purely a guestimation?
How can anyone know the lower limit of the worlds most sensitive human?

If human hearing were any more sensitive, you'd hear the brownian motion of air molecules hitting your eardrums.

 

[Sal1950]

If human hearing were any more sensitive, you'd hear the brownian motion of air molecules hitting your eardrums.

There's a few audiophiles around the media an net claiming those qualities.

 

[sergeauckland]

The way I understand it, 0dB SPL represents the sound level at the threshold of what the best human ear can begin to hear, but it isn't the complete absence of vibrations in the air.

Negative dB SPL is just some level of air pressure variation below that level.

Bear in mind also that the figure of -20.6dB was A weighted. That's 50dB down at 20Hz, so the actual Z weighted i.e. unweighted noise figure could well be (and probably is) above 0dBSPL given that all anechoic chambers lose effectiveness as frequencies get lower as the wedges become comparable and ultimately shorter than the wavelengths involved.


Nevertheless, pretty quiet.
S.

 

[DonH56]

IMO the idea that an audio system, for recording or replay, needs a dynamic range of 123dB is moot.
It would only be necessary if you wanted to make a recording of any sound without adjusting the level control, ie record a trickling stream out in the country and then show up at a rock concert with the same recordewr and microphone and wish to record that too without adjusting the input level. Bonkers.
Same listening at home assuming you never touch the volume control, want even the lowest levels on a recording to be audible and are prepared for permanent hearing damage when a loud bit comes along. Equally bonkers in practice.

In reality, if I am recording a trickling stream out in the country, I will be turning up the levels on my recorder and my limiting factor monitoring the levels will be listening for microphone or other noise in the quiet bits, and the dynamic range - from the loudest trickle to the quietest inter-trickle moment will easily be precisely recorded within 16 bits, never mind 24.
Similarly when I bimble out of the country into a rock concert with my trusty recorder and microphone, when the band is warming up I twiddle the level control - probably a long way down and then, when monitoring (theoretically, headphones won't isolate from the racket enough to monitor levels when in the concert itself) I will be making sure I don't clip. Yet again the difference in loudness between to loudest bits of music and the witty between song dialogue will be easily covered by 16 bits of dynamic range, never mind 24.

So in real sound recordings 16 bit is plenty.
24 bit has the theoretical (and pointless IMHO) benefit of recording every sound there is without adjusting volume - but who in the real world would ever think of doing such a thing?

The difference between theory and practice...

The times I have seen and used 24-bit were in the DAW (studio) world when multiple sources are combined in the mix. If at the same level, each additional source could add another 6 dB, so the extra dynamic range is useful when you start the mixdown process to prevent losing dynamic range. And yes of course it is reduced as you go along, and sources are usually incoherent anyway, but the extra range for processing and mixing is useful IMO. At playback. meh.

 

[stalepie]

When I test online tone generators, like this one http://www.szynalski.com/tone-generator/, I find it fairly easy to hear below 20 Hz without turning up the sound that loud. Is that a result of my headphones being bass boosted, or the source having bass boost? Should I really not be hearing below 20 hz?

 

[Blumlein 88]

When I test online tone generators, like this one http://www.szynalski.com/tone-generator/, I find it fairly easy to hear below 20 Hz without turning up the sound that loud. Is that a result of my headphones being bass boosted, or the source having bass boost? Should I really not be hearing below 20 hz?

There's a good chance your hearing a harmonic and not the fundamental tone.

 

[stalepie]

There's a good chance your hearing a harmonic and not the fundamental tone.

How would I know the difference?

 

[RayDunzl]

How would I know the difference?

Using a sine wave generator (REW as an example), start at say 50 Hz and work your way down.

It should go lower lower lower.

I don't hear a "tone" below about 25-27Hz.

YMMV.

 

[stalepie]

Using a sine wave generator (REW as an example), start at say 50 Hz and work your way down.

It should go lower lower lower.

I don't hear a "tone" below about 25-27Hz.

YMMV.

Isn't http://www.szynalski.com/tone-generator/ a sine wave generator?

I am trying the REW software, but it looks complicated. I'll probably take an hour to figure out how to do a simple test. Already it's giving me some error about not having a sound card set up.

 

[bennetng]

When I test online tone generators, like this one http://www.szynalski.com/tone-generator/, I find it fairly easy to hear below 20 Hz without turning up the sound that loud. Is that a result of my headphones being bass boosted, or the source having bass boost? Should I really not be hearing below 20 hz?

Not very surprising for IEMs. I can even hear down to 8Hz, not that I can hear the actual tone or any harmonic but I can actually count 8 vibrations per second, the change of pressure in my ear canals.

I guess it is because you have physical contact with your headphones.

 

[stalepie]

Not very surprising for IEMs. I can even hear down to 8Hz, not that I can hear the actual tone or any harmonic but I can actually count 8 vibrations per second, the change of pressure in my ear canals.

I guess it is because you have physical contact with your headphones.

Doesn't that mean the redbook standard is inadequate for headphone users? Perhaps when "20 Hz" was measured as a limit, it was done decades ago when we didn't have the equipment yet to measure that low.

 

[bennetng]

Doesn't that mean the redbook standard is inadequate for headphone users? Perhaps when "20 Hz" was measured as a limit, it was done decades ago when we didn't have the equipment yet to measure that low.

The lowest limit is 0Hz (DC) regardless of bit-depth or sample rate. The CDDA format doesn't have a mandatory lowest limit, for example you can burn a 0Hz CDR in CDDA format.

 

[RayDunzl]

Isn't http://www.szynalski.com/tone-generator/ a sine wave generator?

It is...

Using that generator:

PC speakers (external Sony amplified) to microphone, 100Hz:

No harmonics noted. Ambient noise below the red line.

PC speaker to microphone, 30Hz. No longer anything close to a single sine:

Showing strong harmonic content (harmonic distortion) from the speakers.

 

[stalepie]

The lowest limit is 0Hz (DC) regardless of bit-depth or sample rate. The CDDA format doesn't have a mandatory lowest limit, for example you can burn a 0Hz CDR in CDDA format.

Oh OK. I guess I get it mixed up when I think of things I've read, like "The redbook standard was designed around the limits of human hearing, which is roughly 20 Hz to 20 KHz"

 

[stalepie]

It is...

<snip>

Interesting. I guess a lot of musical content I think of is really harmonic distortion, though probably of an intentional sort.

What kind of microphone are you using, though?

 

[RayDunzl]

I guess a lot of musical content I think of is really harmonic distortion, though probably of an intentional sort.

Yes, like, all of it.

There are no musical instruments that I know of that produce a single sine wave.

Exceptions:

Synthesizer.

Blowing on a Beer Bottle comes real close.

My voice, going "Ahhhhhhhhhhh" on a single note:

And going "Oooooooooooooo", with the same fundamental pitch:

 

[stalepie]

Yes, like, all of it.

There are no musical instruments that I know of that produce a single sine wave.

Exceptions:

Synthesizer

And why is a synthesizer an exception? Most of the music I listen to is synthetic

I'd think if it's really most music then, and most music lovers aren't just listening to beer bottles and you saying AHHHHHH then the "distortion" aspects should be included in what people can or can't hear, and human hearing limits shouldn't be measured by pure sine waves alone.

 

[Soniclife]

Interesting. I guess a lot of musical content I think of is really harmonic distortion, though probably of an intentional sort.

Every speaker distorts, at every frequency, but at low frequency the distortion goes up rapidly, look at the below chart, see how the distortion is low across most of the frequency band, but as you go deeper into the bass it shoots up, and this is from a large studio monitor.

 

[Frank Dernie]

Doesn't that mean the redbook standard is inadequate for headphone users? Perhaps when "20 Hz" was measured as a limit, it was done decades ago when we didn't have the equipment yet to measure that low.

Digital can actually go down to DC so no low frequency limit. Don't know if red book limits this technically in any way.
Musical instruments are discerned by the harmonic overtones they add.

 

[stalepie]

Every speaker distorts, at every frequency, but at low frequency the distortion goes up rapidly, look at the below chart, see how the distortion is low across most of the frequency band, but as you go deeper into the bass it shoots up, and this is from a large studio monitor.

Hmm. I wonder why they struggle to get that part right. Maybe they just don't care too since there isn't much musical content down there.