Hello Everyone,
I am back with more dread audio questions that I hope you gurus can help me with. This time I am trying to figure out when to transition from multiple offset domains. In my application, I have an audio input that needs to be cleaned up and then amplified and sent back out to an audio output. Based on what I have read I would expect the following flow of things.
Microphone input: You want to have a DC bias if you're using a capacitive microphone. You have your DC bias added to the input signal and then that is pumped into a preamplifier to make the input usable. At this point we have went from an analog signal based around ground to a offset voltage (let's say 2.5V). Now all our changes are around the 2.5V and then we have a preamplifier that is set to amplify between 5V and 0V. That means our sine wave is now all in the positive territory.
Filtering: That positive signal is now fed into the audio bandpass filter. In my application, I am using a 3rd order Butterworth filter with a sallen-key topography. Now two questions arise from this. One being what do you reference for the sullen key grounds? The other being is what voltage to I use for the op amp supply?
I have done some LTSpice simulations and actually have built the circuit with some different feedback but curious on what the thinking usually is. The application approach I did was to reference the signal grounds to the 0V ground and use a dual supply amplifier from 2.5V to -2.5V. The thought being that the input signal being referenced to ground is already from 5V to 0V but the output for the filter is now being brought back into the dual supply range to be used in the next sections. Maybe this is a terrible way to do this but that's what I am not positive. I can see from one side that things can be clipped because of the dual supply on the op amp. Obviously clipping a signal isn't great. In my application, I do see some clipping if the input gets over 500mV from the input source (microphone). My application can't be hard proof though because I made some changes awhile ago and had some op amps that are made for single supplies set up as dual supplies and had some clipping there.
Since this is a bandpass, it has two or three stages depending on how aggressive you want it to be. In my application, I am using three. If we follow the same flow from above, after the first stage, we have started to come down from the sine wave being around 2.5V to back to ground.
Mixing: This builds on my last question on here about the summing circuit. I understand that part but my question now is built on the above. Do I reference the non inverting input to ground or -2.5V and do I also do a single/dual supply for the amplifier? I am guessing it depends on what my offset is from the filter outputs.
Amplification: My amplifier is designed to take in a signal from 2.5V to -2.5V and amplify it. Its an I2C controller digital amplifier so no filtering or anything needed and I know that part works. At this point, if there is a DC offset, it would have to be removed.
I know this is a wall of text but as you can see, I am kind of lost when to remove the DC offset so signal quality.
I am back with more dread audio questions that I hope you gurus can help me with. This time I am trying to figure out when to transition from multiple offset domains. In my application, I have an audio input that needs to be cleaned up and then amplified and sent back out to an audio output. Based on what I have read I would expect the following flow of things.
Microphone input: You want to have a DC bias if you're using a capacitive microphone. You have your DC bias added to the input signal and then that is pumped into a preamplifier to make the input usable. At this point we have went from an analog signal based around ground to a offset voltage (let's say 2.5V). Now all our changes are around the 2.5V and then we have a preamplifier that is set to amplify between 5V and 0V. That means our sine wave is now all in the positive territory.
Filtering: That positive signal is now fed into the audio bandpass filter. In my application, I am using a 3rd order Butterworth filter with a sallen-key topography. Now two questions arise from this. One being what do you reference for the sullen key grounds? The other being is what voltage to I use for the op amp supply?
I have done some LTSpice simulations and actually have built the circuit with some different feedback but curious on what the thinking usually is. The application approach I did was to reference the signal grounds to the 0V ground and use a dual supply amplifier from 2.5V to -2.5V. The thought being that the input signal being referenced to ground is already from 5V to 0V but the output for the filter is now being brought back into the dual supply range to be used in the next sections. Maybe this is a terrible way to do this but that's what I am not positive. I can see from one side that things can be clipped because of the dual supply on the op amp. Obviously clipping a signal isn't great. In my application, I do see some clipping if the input gets over 500mV from the input source (microphone). My application can't be hard proof though because I made some changes awhile ago and had some op amps that are made for single supplies set up as dual supplies and had some clipping there.
Since this is a bandpass, it has two or three stages depending on how aggressive you want it to be. In my application, I am using three. If we follow the same flow from above, after the first stage, we have started to come down from the sine wave being around 2.5V to back to ground.
Mixing: This builds on my last question on here about the summing circuit. I understand that part but my question now is built on the above. Do I reference the non inverting input to ground or -2.5V and do I also do a single/dual supply for the amplifier? I am guessing it depends on what my offset is from the filter outputs.
Amplification: My amplifier is designed to take in a signal from 2.5V to -2.5V and amplify it. Its an I2C controller digital amplifier so no filtering or anything needed and I know that part works. At this point, if there is a DC offset, it would have to be removed.
I know this is a wall of text but as you can see, I am kind of lost when to remove the DC offset so signal quality.