When I test the mic channel (ADC), does turning the 48V selection on and off make a huge change in the parameters?

[Little Star 233]

I want to test the harmonic distortion and noise floor produced by different audio interface when recording, but I have many questions:
1. What is the difference between the microphone signal and the line out signal? Is the THD+N measured by connecting the line out to the mic interface useful for the actual use of the microphone?
2. Does turning the 48V switch on vs off make a huge difference on THD?
3. When the 48V is not turned on, is the noise floor and harmonic distortion generated by different gears of gain (for example: 0dB, 30dB, 62dB) the same in the line in state as in the 48V mic in state?
4. If I use another DAC to send a 1KHz sine wave to the ADC, is there anything else I need to be aware of? (e.g. will turning on 48V burn the device)

 

[Rja4000]

Does turning the 48V switch on vs off make a huge difference on THD?

Well, probably.
You are likely to destroy your DAC output...

 

[AnalogSteph]

4. If I use another DAC to send a 1KHz sine wave to the ADC, is there anything else I need to be aware of? (e.g. will turning on 48V burn the device)

Not usually, assuming the output is DC-coupled. Given that P48V is current-limited via 6.8 kOhms in series, substantial damage seems unlikely, but output coupling capacitors in AC-coupled outputs may be less than happy depending on voltage rating and polarity. So it kind of depends.

3. When the 48V is not turned on, is the noise floor and harmonic distortion generated by different gears of gain (for example: 0dB, 30dB, 62dB) the same in the line in state as in the 48V mic in state?

The only thing different with P48V on is that the input coupling capacitors are seeing the bias voltage. Their contribution may change accordingly, everything else will behave exactly the same.

2. Does turning the 48V switch on vs off make a huge difference on THD?

Not usually. There might be some change in the bass region.

1. What is the difference between the microphone signal and the line out signal? Is the THD+N measured by connecting the line out to the mic interface useful for the actual use of the microphone?

Line-outs are useful for measuring the THD portion as they can generally output substantial signal amplitudes with ease while providing a low output impedance that's in the same ballpark as a microphone.

You will need substantial (external) passive attenuation if you want to measure input noise accurately at the same time, otherwise output noise is going to swamp input noise by a substantial margin. For example, a balanced attenuator using 2x 4.7k / 2x 75R would provide about 36 dB of attenuation alongside an easily-driven input impedance and close to a standard 150 ohms of output impedance. It is also common to measure the noise with a 150 ohm dummy resistor connected and compare it to a known input signal level.

 

[Little Star 233]

Not usually, assuming the output is DC-coupled. Given that P48V is current-limited via 6.8 kOhms in series, substantial damage seems unlikely, but output coupling capacitors in AC-coupled outputs may be less than happy depending on voltage rating and polarity. So it kind of depends.

The only thing different with P48V on is that the input coupling capacitors are seeing the bias voltage. Their contribution may change accordingly, everything else will behave exactly the same.

Not usually. There might be some change in the bass region.

Line-outs are useful for measuring the THD portion as they can generally output substantial signal amplitudes with ease while providing a low output impedance that's in the same ballpark as a microphone.

You will need substantial (external) passive attenuation if you want to measure input noise accurately at the same time, otherwise output noise is going to swamp input noise by a substantial margin. For example, a balanced attenuator using 2x 4.7k / 2x 75R would provide about 36 dB of attenuation alongside an easily-driven input impedance and close to a standard 150 ohms of output impedance. It is also common to measure the noise with a 150 ohm dummy resistor connected and compare it to a known input signal level.

thank you！ I can use cosmos APU as well right?