Analog Audio Limits


#1

Hello, I am trying to find out what the limits are of the analog input for the BC127. As an experiment, I am inputting a 440 Hz signal into audio input, increasing the amplitude and seeing where the output on some bluetooth speakers begin to saturate. I understand you can adjust the analog gain through “SET AUDIO_ANALOG” but what is the output voltage limit such that you can predict audio clipping from an input? Assuming a 3.3V input.


#2

The 8670 chip gives THD and SNR specs at a 1.6 V peak-to-peak input, so that’s probably a good place to start. That would be after it goes through the gain stage.

I’m not sure if you’re really asking for the ‘output’ voltage limit. If you’re trying to guarantee that the clipping is happening on the input, turn the output gain down very low, then you can be pretty sure the clipping will happen on the input as you step up the input gain. Make sure you start with an input level and gain that gives you a clean signal.

Nick


#3

Hey Nick,

Can you please point me to the datasheet that describes that? My google searching has not come up with that specification for the CSR8670 chip.

As for the output voltage limits, I did do that test, but was trying to quantize it in terms of number to set hard limits. Basically I was asking if you have an input sinwave of peak to peak voltage ‘V’, it will go through the Analog Audio Gain stage ‘G’ resulting in a sinwave of peak to peak voltage ‘GV.’ What is this maximum voltage 'GV’ that will allow the sinwave to keep it’s shape?

Also a quick follow up question, if an audio signal is sent into the audio jack with the board not powered, will this damage the board?

Thanks,
Beau


#4

Yeah, I think the max peak to peak voltage ‘GV’ is around 1.6 volts.
Of course you could easily overload the speaker output with too much gain, even though your input signal is clean.

You won’t damage the unpowered board with an audio signal.