Full Volume Amplitude of Laptop Sound

Discussion in 'The Projects Forum' started by djsfantasi, Apr 11, 2010.

  1. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
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    Is the amplitude of a full volume pure tone from a laptop ±1v or ±1.5v?

    I have an audio to DC envelope circuit and want to spec. out a trim pot for the gain.
     
  2. Bychon

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    Mar 12, 2010
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    You can't expect all laptop computers to use the same audio output circuit. Does this mean you have the computer? If you have it, you can measure it, but you still can't expect all computers to have the same voltage.

    If there is more information that I need, please reply.
     
  3. retched

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    Bychon is right. You best bet is to set up a tone generator (or find a piano program) and ring out a note while measuring the lines with the volume all the way up.
    You may be better served to only turn the volume up until the sound starts to distort, then back off a notch. This will allow any signal you pass to have a cleaner output.
     
  4. JDT

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    Download the Audacity audio editing application. It's free (open source) software. It has a tone generator built-in.

    Best to use an oscilloscope to measure the output voltage. Then you can see the point where distortion occurs. Try at high and low frequencies.

    Test with the load that you are going to use.

    Most PC's will at least produce line voltage: 0.775V RMS with 600 ohm load (0dBm = 1mW into 600ohm)
     
  5. t06afre

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    Different sound cards will have different specifications, and hence behave different. You may fine tune your application to behave deterministic on your computer. But then you move the setup to some other computer the settings will no longer valid. And you have to recalibrate once more. Sound card also tend to drift somewhat. So for accurate measurement you have to do fine tuning every time you turn on your computer.
     
  6. retched

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    Agreed. So adding a pot to your design now will allow you to adjust the input level of your device.
     
  7. djsfantasi

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    All good points,everyone. Thanks. :) It is these different perspectives that I began to think of when I "thought" my design was finished.

    Since the laptop (or potentially other sound source) in question will be used exclusively for running an animatronic, I can set the output level on it.

    I have Audacity, but don't have a scope. Can I measure the output with a DMM? I suppose I could breadboard an envelope follower (which is part of my circuit; the 3 components on the right) and measure the output with the DMM on its output...

    One stereo channel will be feeding the circuit, so I can adjust the gain with R2 (which is actually a trim pot). The circuit rectifies, amplifies and converts the audio to a 0-4vDC envelope of the original signal. In the attached circuit, I plan on using a 200K trim pot in the place of R2, giving me an adjustable gain of 1 to 3 (of which I am convinced...)

    The second channel will be feeding a straight audio amplifier (i.e. LM386 based) and will have a potentiometer to adjust the input level.

    Will these ideas work?

    Thanks,
    dj
     
  8. t06afre

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    Then you are using a DMM it will show the RMS value. Also some DMM is not very accurate then it comes to measuring AC with higher frequencies than say 300-500 Hz. And very often only pure sine waves.
     
  9. djsfantasi

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    Thanks T06afre,

    Frequency of output will be in 85-155Hz range, so a little lower than the 300-500KHz limit.

    The envelope follower circuit will also convert the output to a DC voltage, so I may use that approach as well.
     
    Last edited: Apr 13, 2010
  10. retched

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    I would say that 85-155Hz is a LITTLE lower than 300KHz...

    by a lot.
     
  11. djsfantasi

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    :D

    My point exactly! That range happens to correspond to the typical male voice frequency range, give or take...

    The whole point of this question is part of the design process for a circuit that will take audio of someone speaking and map it to a voltage range whereby a microcontroller can read it with it's ADC and subsequently programatically control a servo-driven animatronic mouth.
     
    Last edited: Apr 13, 2010
  12. Audioguru

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    Consonants of speech range up to 14kHz. Without consonants above 3kHz then speech is just mumble-jumble.
     
  13. t06afre

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    I did not say anything about 300-500 KHz I said Hz:eek: regarding AC volt measurement and DMMs. I think my fluke true RMS meter goes up to about 100Khz then measuring AC (volt)
     
    Last edited: Apr 13, 2010
  14. t06afre

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    So then people talk you in the phone you only hear mumble-jumble ;)
     
  15. retched

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    I was responding to :
    from djsfantasi

    And dont let Rifaa find out you have his Fluke.
     
  16. Audioguru

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    Didn't you read my attachment?
    The consonants are missing on the phone so map and mat sound the same.
    Also faucet and soffet. Pole, coal, goal and hole sound the same. Sailing and failing are two completely different words that sound almost the same on the telephone.

    A telephone line's response is not flat to 3kHz, its is spec'd with a max attenuation of -15dB round trip at 3kHz which is pretty bad. I measured -12dB.
     
  17. t06afre

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    He will never find out I swapped the electronics with a very cheap model from China
     
  18. djsfantasi

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    t06afre - sorry, I thought you said 300Khz... My bad.

    As far as the frequency ranges, I cite the following. There is a difference between the frequencies used for adult speech and the voice frequency band used for telecommunications. The following references document this statement.
    http://www.answers.com/topic/voice-frequency
    http://en.wikipedia.org/wiki/Voice_frequency

    "The voiced speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz[1][2]. Thus, the fundamental frequency of most speech falls below the bottom of the "voice frequency" band as defined below. However, enough of the harmonic series will be present for the missing fundamental to create the impression of hearing the fundamental tone.

    "A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech. In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. It is for this reason that the ultra low frequency band of the electromagnetic spectrum between 300 and 3000 Hz is also referred to as voice frequency (despite the fact that this is electromagnetic energy, not acoustic energy). The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands, allowing a sampling rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN."

    An example of the frequencies used in adult speech, see the chart in the attachment. The following references also document this difference.
    http://hyperphysics.phy-astr.gsu.edu/hbase/sound/earsens.html
    http://www.answers.com/topic/vocal-range
    http://www.answers.com/topic/human-voice
     
  19. Audioguru

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    If you heard somebody talking with only vowels without any important high frequency consonants then you would not know what they are talking about. Just grunts and groans.
     
  20. djsfantasi

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    Thanks, Audioguru.

    Now I get it. It is my mis-read of "Fundamental voice frequency" that was the source of my confusion. I found a paper that described the high consonant frequency range in the 1-3KHz range. I forgot the specific values; the point is it is what you are talking about, no?
     
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