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I've been listening to a test tone CD recently (from www.bcae1.com) and it has been very interesting. The CD is 0dB sine waves at lots of increments. I now have some questions for you knowledgable folks.

Down at 30 hz, I can barely hear the actual note of a test tone. It sounds more like some kind of flapping. However, I have music that goes down in that range (40, 30hz) and I can hear those notes just fine. Why is it that the very low musical notes are visible but the test tones aren't?

Also, I am surprised to discover how high crossover points really are! My own vocal range is about 100hz-800hz. My whistling range is probably 450hz-3khz (although it's hard to judge octaves when you're whistling to test tones). That means that tweeters are crossed over at a very high frequency indeed! It is ear-splitting up there. I haven't listened to slope levels, but it seems like my mids are probably making most of my music.
Vampire has a thread today about staging, where he said his tweeters are high-passed at 5khz. Is there any music that goes much above 5khz? Maybe snare drum beats? And here I was thinking that most vocals came from the tweeters.

Finally, what does it mean that a test tone is 0dB, or -3dB, etc? I know that decibels are a relative measure of volume, so I'm not clear on what the reference point is for test tones.

Thanks in advance, sorry for the long post,

-Dan
 

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0db is the maximum recording level.

If you play a 20-30hz tone and look at it under a spectrum analyzer most of the time you'll see that you're not hearing the tone by itself, but the distortion products at 60hz+.
 

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Discussion Starter · #3 ·
npdang said:
If you play a 20-30hz tone and look at it under a spectrum analyzer most of the time you'll see that you're not hearing the tone by itself, but the distortion products at 60hz+.
Interesting. The players on my computer (Winamp, WMP, etc) have spectrum analyzers but they don't list the frequencies. Is there a free program I can get that has a usable spectrum analyzer?
Or would this be useless, since the distortion you're talking about isn't produced at preamp level, but at speaker level? This is assuming I'm listening to my Grado headphones off my laptop.

Thanks again.

Dan
 

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npdang said:
0db is the maximum recording level.

If you play a 20-30hz tone and look at it under a spectrum analyzer most of the time you'll see that you're not hearing the tone by itself, but the distortion products at 60hz+.

you're also hearing parts of the car resonate :)
 

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Down at 30 hz, I can barely hear the actual note of a test tone. It sounds more like some kind of flapping. However, I have music that goes down in that range (40, 30hz) and I can hear those notes just fine. Why is it that the very low musical notes are visible but the test tones aren't?
Holy back from the dead, Batman! This thread came up in a search I was doing.

Anyway, I happen to know the answer for this.

A sine way is composed of just one frequency, which could be called the fundamental, but there's really no point because there's nothing else there.

A note from an instrument, on the other hand, is composed of the frequency we name the note after (also the lowest frequency in the note), also known as the fundamental, and a train of higher frequencies (harmonics) in differing proportions. It's the proportion of the higher harmonics that allow us to differentiate between a violin, viola, piano, french horn, etc, even when they're all playing concert-a.

So when the big organ on your recording hits that low, low 27.5Hz note (also an A), what you're really hearing is the harmonic train up at pitches like 55 and 110Hz (plus some stuff in between).

Interestingly, a property of psychoaccoustics is that if you play a harmonic train to a human without the fundamental present, the brain will assume it was there and people were have claimed they heard it even though it wasn't there.
 

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Interestingly, a property of psychoaccoustics is that if you play a harmonic train to a human without the fundamental present, the brain will assume it was there and people were have claimed they heard it even though it wasn't there.
...which is how Bose and 'bass boost' features like BBE do their processing - increasing the levels of the lower harmonics and sometimes omitting the fundamental
 
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