What is the noise in the sound output that you hear?
Low level white noise. There are many sources of white noise. There is white noise in the audio track. There can be white noise generated from other components in the stereo system. There needs to be a comparison to a source with less white noise. You can compare the sound with the DAC powered by a SMPS compared to the PurePi ultracap supply or a battery supply. The SMPS powered DAC has more white noise. The background is "blacker" = less white noise with the ultracap or battery supply. The problem is that once you hear your system with less noise, it is very difficult to go back. What to listen for is the first step. For example, dbx has a "pumping noise" as the background noise is increased and decreased with the dynamic expansion process. It is actually difficult to hear unless you know what to listen for. Once you hear it, though, you can't unhear it. It becomes difficult to ignore.
How does the noise get added to the signal?
Not sure. I think it is mostly through the wiring (direct electrical connections). Galvanic isolation can apparently help (no personal experience with this yet). There seems to be very little from radiated EMI. This is based on a setup I had with RPi USB to SPDIF to I2S, which was very quiet. I could not hear the difference between the DAC positioned feet away from the RPI, compared to sitting directly above the RPi.
How does multiple cores add the noise?
Not sure. I assume that each core generates switching noise. More cores = more noise? Using the maxcpus setting would be very informative. At this point, I have only compared different RPis. Noise is lowest in the Zero W. 3B has more noise than a 2B. There could be noise from other sources in the RPi, such as the switching regulators, for example. Greg Stewart (see diyA posts and now at Ian Canada) used to modify the RPi 2s onboard switching regulators to linear regulators for lower noise. The original RPi 1 is known to have low noise, and it has linear regulators, and is also single core.
Low level white noise. There are many sources of white noise. There is white noise in the audio track. There can be white noise generated from other components in the stereo system. There needs to be a comparison to a source with less white noise. You can compare the sound with the DAC powered by a SMPS compared to the PurePi ultracap supply or a battery supply. The SMPS powered DAC has more white noise. The background is "blacker" = less white noise with the ultracap or battery supply. The problem is that once you hear your system with less noise, it is very difficult to go back. What to listen for is the first step. For example, dbx has a "pumping noise" as the background noise is increased and decreased with the dynamic expansion process. It is actually difficult to hear unless you know what to listen for. Once you hear it, though, you can't unhear it. It becomes difficult to ignore.
How does the noise get added to the signal?
Not sure. I think it is mostly through the wiring (direct electrical connections). Galvanic isolation can apparently help (no personal experience with this yet). There seems to be very little from radiated EMI. This is based on a setup I had with RPi USB to SPDIF to I2S, which was very quiet. I could not hear the difference between the DAC positioned feet away from the RPI, compared to sitting directly above the RPi.
How does multiple cores add the noise?
Not sure. I assume that each core generates switching noise. More cores = more noise? Using the maxcpus setting would be very informative. At this point, I have only compared different RPis. Noise is lowest in the Zero W. 3B has more noise than a 2B. There could be noise from other sources in the RPi, such as the switching regulators, for example. Greg Stewart (see diyA posts and now at Ian Canada) used to modify the RPi 2s onboard switching regulators to linear regulators for lower noise. The original RPi 1 is known to have low noise, and it has linear regulators, and is also single core.
Hardware: RPi Zero W | Allo Kali | ProtoDAC TDA1387 X8 | PGA2311 | Icepower 500ASP | Harbeth SHL5
Software: Moode 8.3.3
Source: Win 10 NAS
Software: Moode 8.3.3
Source: Win 10 NAS
