I have a question which google (despite my trying) has not been able to answer. I hope someone here with more knowledge than I would be gracious enough as to correct my understanding on the following point:
I2S data is converted and output by a DAC relative to that specific device's own 0dBFS level and as nothing to do with the voltage the signal was originally sampled at.
example: If an ADC (0dBFS = 2.5Vpp) samples a 1Vpp signal and outputs this signal via I2S to a DAC (0dBFS = 5Vpp), the DAC would output an analog signal at 2Vpp.
Is this correct?
I2S data is converted and output by a DAC relative to that specific device's own 0dBFS level and as nothing to do with the voltage the signal was originally sampled at.
example: If an ADC (0dBFS = 2.5Vpp) samples a 1Vpp signal and outputs this signal via I2S to a DAC (0dBFS = 5Vpp), the DAC would output an analog signal at 2Vpp.
Is this correct?
Good point, sorry about that.
The current setup is designed around a voltage output DAC, however I can not get get the final level required for the project without resorting to large amounts of analog gain (40 dB) after the DAC. This raises the noise floor beyond what is acceptable at lower listening levels. I was hoping to overcome this by utilizing a DAC with a higher output in the first place.
If a current output DAC can offer a significantly higher output and lower noise, I would be happy to consider it.
The current setup is designed around a voltage output DAC, however I can not get get the final level required for the project without resorting to large amounts of analog gain (40 dB) after the DAC. This raises the noise floor beyond what is acceptable at lower listening levels. I was hoping to overcome this by utilizing a DAC with a higher output in the first place.
If a current output DAC can offer a significantly higher output and lower noise, I would be happy to consider it.
monolithic audio DAC, ADC use mixed signal CMOS IC processes - it is handy to use "standard" digital supply V of 5 V, anaolg reference can be close to that in some chips trying for maximum dynamic range, further trying for maximum dynamic range usually involves differential in/out
V output CS4398 DAC is specd as giving 120 dB dynamic range with 6.65 Vpp differential output
you should put a buffer/filter op amp after any audio DAC, differential to SE conversion can include gain
a pretty common desktop consumer digital audio analog output reference level is 2.0 Vrms = 0 dB fs
a technical oddity is that some bit patterns can produce a "over 0 dBfs" on the filtered/reconstructed analog output - a guard band of 3-6 dB would be necessary to avoid this potential problem
V output CS4398 DAC is specd as giving 120 dB dynamic range with 6.65 Vpp differential output
you should put a buffer/filter op amp after any audio DAC, differential to SE conversion can include gain
a pretty common desktop consumer digital audio analog output reference level is 2.0 Vrms = 0 dB fs
a technical oddity is that some bit patterns can produce a "over 0 dBfs" on the filtered/reconstructed analog output - a guard band of 3-6 dB would be necessary to avoid this potential problem
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From what you say about too much noise at lower listening levels, you have the additional gain after the volume control. Moving it prior to the volume control would mean at lower listening levels, the noise also would be lower.
No. It varies from chip to chip. They all require a precision Voltage reference, often provided within the chip. It's pretty common (at least in video) to do fine level trimming by altering the reference Voltage a small amount. You'll just have to read the data sheets to find what you have.
G²
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