merit of 20Khz+ bandwidth in audio effects?

Discussion in 'General Electronics Chat' started by DaveH, Apr 20, 2009.

  1. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    0
    I'm sure people will have opinions on this and this question is basically about opinions from the many knowledgable users on this forum.

    In audio effects for music electronics, it's fairly common to see manufacturers quote 3dB bandwidths of around 20Khz. Even for high end equipment there is rarely much variation. I've got one effect that's rated at 40Khz and it's super cheap. My subjective view of the sound quality is that it's the best gear I've ever used. It's made on the back streets of Taiwan, but I don't care about that.

    People taking a scientific view may say, if an instrument produces measurable harmonics way beyond 20 Khz there is still no point in processing them if the ultimate transducers the listener is using can't reproduce them ie.the loundspeakers for PA, home hi-fi or headphones. Perhaps speakers do still respond slightly at way over 20Khz but it's just massively attenuated?

    They may also say that laboratory tests on humans indicate that very few people can hear anything over 20Khz so that's another reason 40Khz bandwidths are pointless.

    They may also point out that noise power is proportional to bandwidth, so why make it unnecessarily large.

    So what are the arguments in favour of massive audio bandwidths of 40kHz or more? (I've seen some rack mounted processing gear with ratings of 100Khz)

    I think one of them is that despite all the above points against it, the audio transformation is taking place on a broader range of the genuine signal, before being cut down by the transducers at the end of the chain. Though there is no scientific measurable benefit for the listener, they may subjectively have a better experience.
     
  2. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    I'm not sure what the benefit of bandwidth of above 20kHz would be good for, really. I have an audio amp on my bench, along with a function generator. I have experimented with frequency and my own perception of sound. Personally, I can't hear anything above 12kHz even though my amp has plenty of bandwidth. That means my ears are insensitive to any sound having a frequency higher than 12kHz.

    Further, I think that even for those who do hear higher frequencies, those high frequencies are nevertheless attenuated. So what's the point? Maybe dogs appreciate it, but they seem to act like it hurts their ears.
     
  3. leftyretro

    Active Member

    Nov 25, 2008
    394
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    And keep in mind even if you could hear such frequencies, and your speakers can respond, are there any such frequencies in the source music be it CD, FM, Records, etc?

    Edit: I guess you could always listen to a turned up signal generator!
    Lefty
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    There are overtones up there - I am missing around 400 Hz thanks to Navy axial flow blowers, but could still hear tv oscillators up at 15,750 Hz about 15 years ago.
     
  5. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    Turning up the volume on the signal generator? Maybe. But I'm talking about listening to sound at an audible level that does not hurt the ears. ;)
     
  6. DaveH

    Thread Starter Active Member

    Jan 1, 2009
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    I see what you are all saying.

    http://www.tlaudio.co.uk/docs_07/product_07/C-1.shtml

    That piece of gear has 40Khz and it's measured with -1dB, not -3dB!

    There are many other audiophile products and things for recording studios with specs like this. I wonder what the designers were thinking?
     
  7. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    Supertweeters

    The science of acoustics is very complex, and there do seem to be inaudible ultrasonic harmonics that have a noticeable effect on the audible frequencies. It's one of the reasons why CD, with its 20 kHz brick-wall lowpass filter, doesn't sound as good as a really good analogue recording with a higher bandwidth.

    If this sounds a bit like voodoo, then that's quite understandable, I'd demand a demo to be properly convinced. But consider a couple of examples: (1) The use of ultrasonic beams to make a highly directional speaker [EDN], and (2) the ability of a small number of people to hear the 'singing' of switched mode power supplies, operating way above the audio band. With the latter this often comes about as a consequence of tinnitus, in particular a type of high-frequency tinnitus that is also normally above the HF hearing threshold. The ultrasonic tinnitus signal mixes with the ultrasonic power supply noise, and the non-linear response of the ear produces intermodulation products down in the audible frequency range. Usually the unfortunate sufferer is at a loss to explain why no-one else can hear the noise that is driving them mad, and that is so obviously coming from the DVD player, or wherever.
     
  8. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    Oh yes, and as far as amps going beyond 20 kHz are concerned, that's mostly to do with obtaining a good transient response and a linear phase shift in the audio band. But sometimes it's specmanship.
     
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