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  1. #1
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    Questions about infrasound

    Hello, can anyone tell me if I'm going the right way about producing infrasound / ultrasound tones?

    I have a generic audio editor which has a noise generating facility, this asks for a base frequency, a frequency to modulate by, then a "modulation frequency" and start phase.

    I fill in all of these as ZERO except for the Base Frequency, which is the infrasound / ultrasound tone I want to generate. Is this correct?

    Then it wants to know whether to modulate or demodulate (I do neither) and flavour (Sine). Is all this A.O.K?

    What I'm trying to do is generate the specific infrasound tones associated with haunted houses (18.98 HZ) - if anyone knows a better way, especially of reproducing them, I'd love to know.

    Also - how good is most sound reproduction equipent at actually generating the sounds? What are the optimal settings on a home hi-fi for generating infrasound - in say, volume, bass and treble? I've noticed for example that my computer speakers shift the frequency of infra tones up into the audible range at between 10% and 40% volume - what kind of speakers should I buy to generate the tones, or should I even attempt to build one myself?

    Finally I come to media - I'm generating 16-bit, mono WAV files at a sample rate of 48000 - is this good enough? My hi-fi rig is an old valve amp seperates, and I've got a choice of running an MP3 player or transcribing the tones to cassette tape - which would a proper sound engineer choose? And wouldn't mp3 compression tend to kill the infra? Parameters?

    If anyone could answer any of these questions, I'd be much obliged....

  2. #2
    So, what does a haunted house sound like? Sounds like you are trying to build a waveform from scratch, starting with a sine wave (pure tone, no harmonics, unpleasing to the ear) and then add and subtract harmonics to achieve the tone you want. This is called "Fourier Synthesis".

    Gotta go for a moment. I'll get back.

    I am not quite sure how that would work on your generator, but my guess is that the modulator and demodulator are how you would add and subtract those harmonics. But I think you would be better off finding a sample from a library on-line to use, at least as a starting point, mainly because fourier synthesis is a science in and of itself, and without a harmonic map it would be hit and miss to build the sounds you want. If you hit on it please let me know how you did it.

    As far as speakers go, you're talking below the generally excepted range of hearing, called subsonic. You would need a subwoofer with a seperate amp channel and low pass filter to get anything like a movie theatre rumble effect. Surround sound comes to mind, but would require recording software for it.

    16 bit @ 48kbps is fine, (32 @96k is better),but skip cassete tape and master to mp3 if those are your choices. Compression could be a problem there but I'm not sure what, and there are ways of dealing with it. I'll have to look it up.
    Last edited by penniesfromheaven; 2nd Apr 2007 at 19:49. Reason: (back)
    'I think my intimate relationship with electronics started as a child when I was playing with a screwdriver and a wall plug, Doc, and...'

  3. #3
    There are software tools that may help with the compression problem. Blaze Media Pro is one that offers alot of conversion options. There are quite a few out there. Compression problems in my limited experience are mainly due to how you convert from one media to another.

    Gotta go again.
    'I think my intimate relationship with electronics started as a child when I was playing with a screwdriver and a wall plug, Doc, and...'

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