PCM2902C: PCM2902C Low Input Volume

Hi, Steven,

Welcome to E2E, thanks for your interest in our products.

It is possible that the software used to record audio from the codec has different gain settings. I have seen Windows adding a +20dB gain if the codec is detected as mic input device, not line input device. Do you see a difference on the waveform captured with one or other software? Or, is the only difference the amplitude of the signal?.

Can you please provide more information about the test procedure so I can try replicating it in my EVM?.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Diego, 

Thanks for reply..

I have done comparison tests on both iMac and Windows 7 with similar result. 

Today I did a comparison on Windows between a regular sound card the PCM2902C and using an audio recording program called Intune http://www.gammaspectacular.com/marek/intune/index.html

This recording software displays the dynamic range in arbitrary units -100 to +100 arb.u.

The volume ratio between the TI codec to sound card was 6/100

The only difference in the waveform in this case was that the sound card inverted the pulse.

Hi, Steven, 

Thanks for the feedback. With the information provided it is still unclear why the input of the PCM2902C has a low amplitude, because the input signal you are providing is aligned with the expected for a full-scale output on the digital side.

I tested the EVM in a recording application using audacity, a 2Vpp input signal was applied to the EVM input and I was able to get a full-scale digital signal. 

This makes me think that this issue is caused by an incorrect setting of the device configuration by the OS.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

 I tested the codec again today with Audacity, this time I hooked up my scope across V common pin 14 and V Left input  pin 12, and adjusted my pulser to just under  Vpp 2.0V.

On the attached image you can see that the digital signal barely makes it above 0.1 on the vertical scale. 

I am using 3.3V regulated supply on pin 10 (Vcci) and VBus 5.0V on pin 3.

The volume from my circuit is similar to the evaluation module and across both my Mac and Windows computers. 

Pulse height resolution is critical to my application , so any suggestions would be welcome. 

Steven

Hi, Steven,

Thanks for the feedback. I am wondering if this issue has something to do with the input configuration you are using. Is it possible to share your schematics?. Why are you measuring the input signal across VIN and VCOM?. Typically, a GND centered signal is provided to the analog inputs before the decoupling cap.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer