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Clear Voice!!


Andres Ramos

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Very amazing result that came up more as a byproduct today. I was tinkering around with WavePad, not because I intended to do a serious ITC session but just to learn more about WavePad itself. As I wrote in my main blog I discontinued working with Audacity for certain reasons.

I was checking the amazing video export function in WavePad where you can export an audio track in real time animation with it's sound. As I checked the result I suddenly heared a crystal clear voice. In fact it was so clear that first I thought my wife had spoken to me. But then I saw the waveform in the video and could identify and play it back again an again.

The voice is at video position 12s. I cut the video to repeat the crucial sequence two times.

Here is the video:

The voice says something that sounds like "Most" or "Mose" in english or maybe "Maus" in german. Voice: Most.mp3

This type of voices I only know as direct microphone voices but I had used no microphones.

 

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What an amazing capture Andres. Yes, it doesnt seem to fit with the background - like as you say, someone speaking into a microphone. Are you saying that the export process itself generated this voice?

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9 hours ago, Dr Jeffers said:

What an amazing capture Andres. Yes, it doesnt seem to fit with the background - like as you say, someone speaking into a microphone. Are you saying that the export process itself generated this voice?

I had the same thought but the voice is already in the original recording. It's the same phenomenon like the voice saying "Jenny" you discovered in my previous clip. It has a characteristic that is different. Generally the voices in the carbon clips are distorted and spiky. You have to make them intelligible by applying reverb and filters. The other voices are very clear, like gained with a microphoneand in fact I remember those voices ONLY from my experiments with direct voices where I used a condenser electret microphone with a self designed preamplifier.

But here the crucial question comes up again; if we record direct microphone voices, do they really com THROUGH the microphone or are they using another way? It's strange since I had planned to do investigations on direct microphone voices before the carbon thing came up again.

If we are suggesting that natural sounding voices can manifest without a microphone the question arises how they do that? I am hypothesizing that this is the point where Hodowanec comes into play again. What if they are coming in through a capacitor?

 

Hodowanec.jpg

The capacitor C2 is a polarized cap like Hodowanec used them and it is in the feedback network of the OpAmp. Thus electrical fluctuations in the capacitor will scale up at the output of the OpAmp. With P1 set to a low value you almost have the Hodowanec circuit here.

 

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Yes, this is a possibility. The value of the capacitor and the value of the 1K pot are variables that will kindle the Hodowanec effect.

As youve implied, with P1 trending to zero ohms, there is maximised Hodowanec effect, and the stage therefore reverts to being a standard transimpedance amplifer, but of course the extremely high gain is unusable within the present application.

What Id like to suggest to test is this:

To construct another separate non-inverting op amp stage fed from T2 collector as is the original one, but this second stage has a differing value of P1 with a chosen value of R4 (so both gains of the amps are equivalent). Compare the two channels of outputs to see if a changed value of P1 causes more or less  PK modulation.

Another test would be to have identical values for P1 and R4 for both amps, but change C2 in one amp to see if there is difference.

[ Time for bed for me! ]

Edited by Dr Jeffers
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1 hour ago, Dr Jeffers said:

Yes, this is a possibility. The value of the capacitor and the value of the 1K pot are variables that will kindle the Hodowanec effect.

As youve implied, with P1 trending to zero ohms, there is maximised Hodowanec effect, and the stage therefore reverts to being a standard transimpedance amplifer, but of course the extremely high gain is unusable within the present application.

What Id like to suggest to test is this:

To construct another separate non-inverting op amp stage fed from T2 collector as is the original one, but this second stage has a differing value of P1 with a chosen value of R4 (so both gains of the amps are equivalent). Compare the two channels of outputs to see if a changed value of P1 causes more or less  PK modulation.

Another test would be to have identical values for P1 and R4 for both amps, but change C2 in one amp to see if there is difference.

[ Time for bed for me! ]

Yes I see, a good idea. What I have done today was to connect the + input of the OpAmp directly to the middle of the power supply with no signal input for the OpAmp. Then I looked for pk modulation. In a 2nd run I enlarged the capacitor upt to 2200uF. In both cases I had no pk modulation. To be sure I need to make longer test runs of course.

 

Have a good night, Jeff!

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To receive some hodowanec noise from the C2 capacitor Andres - with the reference volts applied to (+) input, youll need to have P1 as a short circuit, so the amp can function fully to amplify the picoamp currents coming from C2.

Having P1 in cct will greatly attenuate the gain, depending on what the value of it is.

If you want to try an experimental Hodowanec cct, I can give you values from a TIA calculator:

OpAmp: TLO81 or similar 4MHz GBW, FET i/p

Input cap 1,000uF (direct to inverting input - no input resistor).

Feedback resistor 1,000 ohms.

Feedback capacitor 2.2uF (across the 1k resistor)

These values give a stabilised bandwidth of 8.7kHz. Gain is 53dB.

Values obtained from calculator are for the 1,000uF cap value. I have not tried these values, but have experimented with his circuits and they do produce copious noises, some of which are interesting.

In regards the Hodowanec effect with coherer noise input, I theorise that the Hodowanec effect works on the noise input, so it is a balancing act of input noise fed to it - verses noise received from the capacitor itself as a receptor. The sweet spot is to get the Hodowanec effect to pk modulate the incoming noise, without burying it. This is the reason I suggested you run 2 amps from T2 collector, and have differing values of P2, but have equal gains via R4 selection, so as to do comparisons in pk modulation efficiency / clarity of voices. It is presumed a lower value of P2 will yield better pk mod compared to a higher value, so this can be checked by comparison.

This sweet spot fine tuning is something I was experimenting with some months ago. Have not done any work on it recently due to other commitments.

Edited by Dr Jeffers
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Thanks for your very clear advises Jeff! I have everything on stock what you listed. If I get you right then the reason for comparing those two amplifiers, with equal gain,  is that decreasing P1 makes the circuit more "Hodowanec" and increasing makes it less?

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Yes, Andres, thats exactly right.  The real test will be how low in value you can get P1 in one channel while still maintaining good operation.

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