PCM5242: SNR test conditions

Hi Amy,  it is mentioning the A-weighted filter was used for this measurement, It is  at the output of the filter.

Regards,

Arash

Hi Arash,

Sorry, at first I didn't understand the meaning of A-weighted. Now I know that the SNR measured by the customer is also A-weighted, but it is lower than that in the datasheet. What may be the reason for this?

Best Regards,

Amy

Hi Amy, When you say SNR is lower , what is the value that they are getting?

Also please remember SNR is a measurement that describes how much noise is in the output of a device in relation to the signal level, so it is dependent on signal level.

Another question is how they are measuring SNR? are they using AP?

Regards,

Arash

Hi Arash,

The customer's test results are shown in the figure below. The left channel SNR (A-weighted) is 72.8 dB. The right channel SNR (A-weighted) is  72dB. 

The specific steps of the test are as follows:

(1) Turn on the tested sample and adjust the media playback volume to the maximum;

(2) The audio output terminal of the tested sample is 3.5mm audio interface, insert a cable (32 Ω resistance), and the other end of the cable is connected to the audio analyzer;

(3) The measured sample plays a 1kHz, 0dB sound source and measures the amplitude of the output signal;

(4)  The measured sample plays the mute file and measure the amplitude of the output signal.

(5) Calculate the signal-to-noise ratio.

Best Regards,

Amy

Hi Amy, Have  they measure the noise floor by duplicating  Figure 16. 1 or other figures in DS,  may be they would see that their noise floor is much higher than what is expected .  If so, I  would say their board  and setup( routing and cables) needs to be checked and optimized. 

Another possibility is that there is an attenuation of input signal and they are not really sending 0db as their input. 

SNR is made up these two components and one or the other is not what they think it is.

Regards,

Arash