Why is it that an amplitude-scaled sound does not play louder than the original sound using Play Waveform?

[armil]

I don't know if I have posted this on a correct location (kinda new here).

I am trying to demonstrate the effect of multiplying a constant to a waveform. I have a sound file read by Sound File Read Simple.vi. Then I am trying to scale the amplitude of the signal by a constant number. I've tried three methods for this: the Numeric Multiplication, the express VI Scaling and Mapping, and the scaling and conversion VI of Signal Express. The waveform shows that the amplitude of the scaled signal is indeed scaled, but when played thru the play waveform VI, the sound level is still the same, no matter how much I am scaling the input. Does anyone why is this so? Also, I really wanted to show that scaling an audio waveform results in a louder waveform. How do I do this? As much as possible, I've wanted to use simple VIs as the class is an introduction to signal processing and the students (and so am I) are still finding our way into LabVIEW (we used to use MATLAB in the course).

[Coq_Rouge]

Are you the Teacher in this class?

[Coq_Rouge]

By the way the data sent to the sound card is normalized by the Labview functions. So using the scale Express VI. Will not affect the sound volume.

[kirkbardini]

I´m having the same problem. Is that a way to amplify the sound on speakers? I´m working on a low frequency signal (100-300hz). Actually I have a PCG signal and I need to listen to the heart sound on the speakers. Anybody knows how can I do this?

Best regards,

[JaymeW]

Hi kirkbardini,

According to this article about Low Volume From Sound VI, you can use a scalar multiple to increase the volume of a sound saved to a .wav file, so you should be able to do this before playing it.  Does that not work for you?

[Coq_Rouge]

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@JaymeW wrote:

Hi kirkbardini,

According to this article about Low Volume From Sound VI, you can use a scalar multiple to increase the volume of a sound saved to a .wav file, so you should be able to do this before playing it.  Does that not work for you?

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That information is for Labview 7.x and hence outdated. As mentioned before. Labview do a normalization before sending data to the sound card. As you know sound cards are most often 16 or 24 bits. And in most cases data input to a sound card is in DBL type. After normalization the data is converted so the floating point value 1 represent full scale output on data sent to the the sound card DA. To get any further I suggest kirkbardini take the time needed to send us his/hers current code. Then we may solve things from there

[kirkbardini]

Coq Rouge and JaymeW, thank you for answering my question.

JaymeW,

I tried increase the volume using a scalar multiple, but it didn't work.

Coq Rouge,

I'm working with LabVIEW 2011, so this explains why the use of a scalar multiple didn't work. Thank you!

Now I don't have the current code here with me. I can send you the code tonight when I am at home.

Regards,