Cannot understand the attenuation in signal as the audio bit depth of adc changes I am working on Active Noise Cancellation Project. I came across this strange problem, where the signal is getting attenuated as the audio bit depth changes and I cannot understand it!
My circutit :I connected Audio Output( Head phone terminal) of PC to Audio IN of NI myRIO 1900 device using AUX cable (two way 3.5mm jack cable). I have a pre-recorded signal(.wav) of sinusoidal waveform with Amplitude 1, Frequency 2kHz, 40000 Sample Rate, 80 Number of Samples, Bit depth( bits per sample) = 16.
Now, I just played .wav file using windows media player and tried to record the waveform on NI myRIO module. Surprisingly, I am getting an attenuation of the signal corresponding to the volume reduction in PC(not linear!!). Only I could see the waveform close to amplitude 1, when I increased the volume of the system to 100%. Please explain this !!  

The ADC of NI myRIO has its Resolution as 12 bits but the audio Output(.wav file) is 16 bit data. I am expecting it does not have to matter except in quantization errors, as at the PC Audio Out, the audio data should be converted to analog and and again at the 'NI myRIO Audio In', this analog signal will be sampled! (please correct me if I am wrong !)
Another question is, I have tried the same with sinusoidal sound of Amplitude 2.5 and all other specifications are same as given above, now the audio signal is clipped off at 1V above and below -1V.

 ADC(NI myRIO) nominal range is 2.499V to -2.5V! Is it bacause of the bit depth conversion?
Please explain these things !TQ
From NI myRIO-1900 User Guide and Specifications:


  The audio inputs are left and right stereo line-level inputs with a
  ±2.5 V full-scale range
  
  • For Audio In/Out, 
  LSB Weight = 5 V ÷ 212 = 1.221 mV 
  Maximum Positive Reading = +2047 * 1.221 mV = 2.499 V 
  Maximum Negative Reading = -2048 * 1.221 mV = -2.500 V


Your computer's head phone output probably has another constant of proportionality between voltage and numerical value. Perhaps you can find manufacturer's data, but it is probably safer to simply measure with the help of your NI device.