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"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 00:11:36 +0000, Laurence Payne
wrote: On Sun, 18 Jan 2004 22:36:52 +0000, Chris Isbell wrote: Simple addition of two frequencies does NOT result in any new frequencies. Only non-linearities causing one of the signals to be multiplied by the other (aka 'mixing', 'modulating' or 'heterodyning') will cause sum and difference frequencies to be created. That poses the question, how can I tune instruments accurately using beat frequencies? If you want them to be "perfectly" (and I use that term precisely) in tune, you tune for zero beats. This is quite easy for unisons and octaves, takes a bit of practice for 5ths and 4ths. [snip] Sorry you asked? :-) No, I could go on at great length about tuning and pitch. ;-) The question I was trying to get at was that it the chain from the instrument to my ear/brain is substantially linear, then why do I hear beat frequencies? (If it is not linear, then why is linearity such a concern for Hi-Fi systems?) [Off topic: Many years ago when I was actively involved in playing early woodwind instruments, the group I was playing with did some interesting experiments in using 'just intonation' and changing the tuning whenever the music modulated. Thus we were going for zero beats - not that easy on a sopranino recorder.] -- Chris Isbell Southampton UK |
"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 09:32:32 +0000
Don Pearce wrote: Try 400 and 401 Hz then - far more obvious. You do not hear a tone at 1Hz in these circumstances - you hear beats. These are very different. There is no tone, there is no need for any non-linearity that might generate a tone. You are simply hearing pressure peaks moving in and out of phase. Its the same effect though. I agree 1 Hz isnt really a tone, but it is a signal. Or are you suggesting that the pressure peaks DONT move in and outr of phase in the 400/450 case? -- Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup. |
"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 11:24:37 +0000, Ian Molton wrote:
On Mon, 19 Jan 2004 09:32:32 +0000 Don Pearce wrote: Try 400 and 401 Hz then - far more obvious. You do not hear a tone at 1Hz in these circumstances - you hear beats. These are very different. There is no tone, there is no need for any non-linearity that might generate a tone. You are simply hearing pressure peaks moving in and out of phase. Its the same effect though. I agree 1 Hz isnt really a tone, but it is a signal. No, it is not even a signal. There is a variation in level at 1Hz, but absolutely no acoustic energy whatever at that frequency. Have a look at the two tones on a spectrum analyser and try to find anything at all going on at 1Hz - you won't find it. Or are you suggesting that the pressure peaks DONT move in and outr of phase in the 400/450 case? Of course they do. d _____________________________ http://www.pearce.uk.com |
"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 08:14:10 +0000, Ian Molton wrote:
On Mon, 19 Jan 2004 08:05:13 +0000 (UTC) (Stewart Pinkerton) wrote: Um, you think that he can hear a 1Hz tone more easily than a 50Hz tone? From which planet are you connected to the Internet? a 1 Hz beat frequency? you bet. Unfortunately, you've no ideea what you're talking about. That 1Hz beat frequency is an envelope effect modulating the amplitude of the originals, and it doesn't exist in linear systems. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 11:24:37 +0000, Ian Molton wrote:
On Mon, 19 Jan 2004 09:32:32 +0000 Don Pearce wrote: Try 400 and 401 Hz then - far more obvious. You do not hear a tone at 1Hz in these circumstances - you hear beats. These are very different. There is no tone, there is no need for any non-linearity that might generate a tone. You are simply hearing pressure peaks moving in and out of phase. Its the same effect though. No, it absolutely is *not* the same effect. I agree 1 Hz isnt really a tone, but it is a signal. Or are you suggesting that the pressure peaks DONT move in and outr of phase in the 400/450 case? This only occurs if you have two separate *sound* sources, it does *not* occur in a linear system with a single speaker. It works for piano tuning, but not for amplifiers.............. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 08:05:13 +0000 (UTC),
(Stewart Pinkerton) wrote: Try 400 and 401 Hz then - far more obvious. Um, you think that he can hear a 1Hz tone more easily than a 50Hz tone? From which planet are you connected to the Internet? You can, and will, hear a 1Hz beat. Piano tuners do it every day. |
"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 09:42:43 +0000, Chris Isbell
wrote: No, I could go on at great length about tuning and pitch. ;-) The question I was trying to get at was that it the chain from the instrument to my ear/brain is substantially linear, then why do I hear beat frequencies? (If it is not linear, then why is linearity such a concern for Hi-Fi systems?) How did we get sidetracked into this "linear" argument? You hear beats because they are a simple physical result of mixing two sounds of close pitch. That's it. If you set up a series of pitches approximating to the overtones of a low note, your brain will sometimes "hear" the low note. This isn't mumbo-jumbo, it's an established technique in church organ construction, and probably elsewhere. But it's nothing to do with beats. |
"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 11:37:26 +0000, Don Pearce
wrote: Its the same effect though. I agree 1 Hz isnt really a tone, but it is a signal. No, it is not even a signal. There is a variation in level at 1Hz, but absolutely no acoustic energy whatever at that frequency. Have a look at the two tones on a spectrum analyser and try to find anything at all going on at 1Hz - you won't find it. You can hear it though, can't you. Are you troubled by being able to hear a variation in level - sometimes called a tremolo (did I spell that right?) |
"What HiFi" - can it be trusted?
On Mon, 19 Jan 2004 18:31:45 +0000, Laurence Payne
wrote: On Mon, 19 Jan 2004 11:37:26 +0000, Don Pearce wrote: Its the same effect though. I agree 1 Hz isnt really a tone, but it is a signal. No, it is not even a signal. There is a variation in level at 1Hz, but absolutely no acoustic energy whatever at that frequency. Have a look at the two tones on a spectrum analyser and try to find anything at all going on at 1Hz - you won't find it. You can hear it though, can't you. Are you troubled by being able to hear a variation in level - sometimes called a tremolo (did I spell that right?) Yes a variation in level - but no tone, and very specifically, no signal. It simply isn't there to be heard. d _____________________________ http://www.pearce.uk.com |
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