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Improve Raspberry 4 streamer

Gekel

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Reading links you have posted seems to be better to underclock Raspberry cpu to have less output noise? Correct?
no. And why should the CPU frequency affect the sound quality? Are you sure you are on the right board? I would ask ppl on audiophile if you believe in this here...
 

audio_tony

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I am considering building a Raspberry 4 streamer with a DAC hat or separate board of some kind. It would be nice to have a small combined streamer and DAC.

I believe one of the main issues with having a DAC in the same box is perhaps power supply noise coming from the wall USB switching power supply or the Raspberry microprocessor. I am thinking of powering the DAC separately using a rechargeable battery with a linear voltage regulator. There might be an off the shelf USB power pack that would work. Or maybe an LT3045, or similar ultra low Noise switching regulator that separately powers the DAC hat. Has anyone tried this separate power supply approach?

Off the shelf USB power packs use a switching regulator to make 5V from the battery voltage. Many of the DAC boards use multiple regulators, including a switching one to make the -ve voltage rail for the output opamps. You need to look at the specifics to see if a separate PSU will improve anything.

Good point,


Good point, "Off the shelf USB power packs use a switching regulator to make 5V from the battery voltage", which could reintroduce noise that you were trying to reduce. You would need the battery directly connected to a linear power supply and bypass the switching regulator.

I performed some tests on a Raspberry Pi4 and the 'official' Pi PSU and a linear PSU. There was little between the two in terms of noise.

The biggest issue as ever, is one of ground loops, which do create noise.

There are too many images to post here so take a look at my measurements on my site: https://gtkc.net/usb-noise-measurements
 
OP
officialsm

officialsm

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I performed some tests on a Raspberry Pi4 and the 'official' Pi PSU and a linear PSU. There was little between the two in terms of noise.

The biggest issue as ever, is one of ground loops, which do create noise.

There are too many images to post here so take a look at my measurements on my site: https://gtkc.net/usb-noise-measurements

Thank you, could you explain here results of your tests and which is better configuration?
 

audio_tony

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Thank you, could you explain here results of your tests and which is better configuration?

In summary:
The column with the highest SINAD figure is the one of interest and the 'best'.
When powered by the linear PSU, the Pi is 1.48dB quieter than running with the official PSU. (in other words - this is of ZERO consequence).
It's slightly quieter still on battery, by 1.77dB, again of no consequence.
The results of a ground loop are shown in the bottom row where it can be seen that SINAD is reduced by 32.4dB - this may be audible at very high volume (and I'm thinking full volume) but that depends on several factors, amp power and preamp gain etc.

Ultimately, it's highly unlikely that anybody would be able to hear any difference between the Pi running on battery, linear PSU or official PSU.
So as long as you buy a decent PSU (doesn't need to be linear, and ideally isolated from ground) you'll be fine.

The sound quality does not change.

1623249161149.png


*NOTE: the slightly inferior noise figure above when using the isolated ADC is a function of the ADC itself - and not the noise figure worsening.
 

xaviescacs

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In summary:
The column with the highest SINAD figure is the one of interest and the 'best'.
When powered by the linear PSU, the Pi is 1.48dB quieter than running with the official PSU. (in other words - this is of ZERO consequence).
It's slightly quieter still on battery, by 1.77dB, again of no consequence.
The results of a ground loop are shown in the bottom row where it can be seen that SINAD is reduced by 32.4dB - this may be audible at very high volume (and I'm thinking full volume) but that depends on several factors, amp power and preamp gain etc.

Ultimately, it's highly unlikely that anybody would be able to hear any difference between the Pi running on battery, linear PSU or official PSU.
So as long as you buy a decent PSU (doesn't need to be linear, and ideally isolated from ground) you'll be fine.

The sound quality does not change.

View attachment 134691

*NOTE: the slightly inferior noise figure above when using the isolated ADC is a function of the ADC itself - and not the noise figure worsening.
This is outstanding work! Just a question, which is the best SINAD you have measured in your DAC? I assume is quite close to the best SINAD in this table, but just to be sure. Thanks!
 

audio_tony

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This is outstanding work! Just a question, which is the best SINAD you have measured in your DAC? I assume is quite close to the best SINAD in this table, but just to be sure. Thanks!

Thanks. I usually get around 104dB to 106dB SINAD - depending on how much effort I put into ensuring there are no stray cables / hum fields!
 

Jinjuku

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In summary:
The column with the highest SINAD figure is the one of interest and the 'best'.
When powered by the linear PSU, the Pi is 1.48dB quieter than running with the official PSU. (in other words - this is of ZERO consequence).
It's slightly quieter still on battery, by 1.77dB, again of no consequence.
The results of a ground loop are shown in the bottom row where it can be seen that SINAD is reduced by 32.4dB - this may be audible at very high volume (and I'm thinking full volume) but that depends on several factors, amp power and preamp gain etc.

Ultimately, it's highly unlikely that anybody would be able to hear any difference between the Pi running on battery, linear PSU or official PSU.
So as long as you buy a decent PSU (doesn't need to be linear, and ideally isolated from ground) you'll be fine.

The sound quality does not change.

View attachment 134691

*NOTE: the slightly inferior noise figure above when using the isolated ADC is a function of the ADC itself - and not the noise figure worsening.
Thanks for the efforts and mirrors my own experimentation with an RME ADC.

No need to spend $600 on a custom endpoint that actually has more limitations than a Pi 4.
 
Last edited:

reprap

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Hi I want to replace the usb cable between my Pi4 and Pontus 2 usb.
Is there a wifi or bluetooth dongle pair that can replace the cable?
I don't want to use the Pi internal wifi to reduce cpu load.
Any ideas?
 

somebodyelse

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Hi I want to replace the usb cable between my Pi4 and Pontus 2 usb.
Is there a wifi or bluetooth dongle pair that can replace the cable?
I don't want to use the Pi internal wifi to reduce cpu load.
Any ideas?
What exactly are you hopping to improve by changing the USB cable, and what makes you think some dongle pair would be an improvement?
 

antcollinet

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Do you think something like IFI PURIFIER added on usb could helps?
No.

If you are using audio directly out of the raspberry pi, then a much better solution would be a proper DAC hat - or even better an external USB DAC (good** external DACs tend to measure much better than Hats).

You won't get any audible benefits from any other tweaks to your pi in the digital domain (before conversion to analogue) unless you are getting gross errors in the audio to indicate digital errors (pops clicks, or drop outs)


**(good, not expensive - an important distinction. Even the $10 apple dongle measures exceptionally well)
 

antcollinet

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What exactly are you hopping to improve by changing the USB cable, and what makes you think some dongle pair would be an improvement?
1 - why worry about CPU load? The Pi4 has more than enough power for audio applications. I'm not even sure the Pi 4 is particularly stressed by its wifi interface anyway.

2 - Seconding @somebodyelse 's question - what are you trying to achieve?

3 - You could use a second raspberry pi running a simple airplay receiver (assuiming whatever streamer software you are using supports airplay). Even a zero 2W would suffice.
 

reprap

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Thanks for your help here.
My first goal is complete galvanic isolation from the Pi.
Second is to reduce cable runs across the lounge room and keep the wife happy.
Thirdly reduce ground loops, and forth stop floating power supplies from adding 110v to my data stream.
Its not really the cpu load, its the noise of more processes running that aren't essential for playing music.
I have an excellent Imac running HQ Player or Pure music. It also is doing gazillions of other things that muddy the music output. My Pi4 LMS server and separate Pi4 Pi core player deliver a much cleaner signal to my Pontus 2 Dac than the IMac ever did.

Simplistically I am looking for a USB Bridge where each end is powered from it's USB port. The two dongles are paired and are not part of a mass of data traffic and noise on my router.
What can you recommend?
 

somebodyelse

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The Pontus 2 is claimed to have galvanic isolation for all digital inputs anyway, so unless it's a lie you already have that. It should also break any USB-related ground loop. If you don't like the idea of a floating PSU then get one that's ground referenced. The only thing left is removing a cable run - is there any reason not to put the player Pi next to the DAC while connecting to the same wifi network as the server?
 
F

freemansteve

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If you are connecting a Pi over WiFi, unless you are near to your WiFi router/bridge, be wary of putting the Pi in a metal case.
You can get quite a fall in (WiFi) signal strength, which may force network retries, and sound issues, if it gets really bad. Especially so if you run in the 5GHz band.

There is a way to disconnect the PCB-track-based antenna and run an external antenna, or you can use the Pi development motherboard which allows for an external antenna with no mods. The case footprint is a lot bigger, but you can easily use big heatsinks in it, if you need. Lots of info on the 'net about this.
 

antcollinet

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Thanks for your help here.
My first goal is complete galvanic isolation from the Pi.
Second is to reduce cable runs across the lounge room and keep the wife happy.
Thirdly reduce ground loops, and forth stop floating power supplies from adding 110v to my data stream.
Its not really the cpu load, its the noise of more processes running that aren't essential for playing music.
I have an excellent Imac running HQ Player or Pure music. It also is doing gazillions of other things that muddy the music output. My Pi4 LMS server and separate Pi4 Pi core player deliver a much cleaner signal to my Pontus 2 Dac than the IMac ever did.

Simplistically I am looking for a USB Bridge where each end is powered from it's USB port. The two dongles are paired and are not part of a mass of data traffic and noise on my router.
What can you recommend?
Nothing your PC or PI can do in terms of load or other processes can "muddy" the sound of a digitial signal. If errors are introduced into the digital data it won't impact the frequency response, or any other subtle change to your music. It will result in gross effects such as drop outs or pops/clicks.

Further - your PC is designed to move vast quantities of data around it's subsystems without errors. If it cant do that, then it can't function at all. It would crash all the time.

It *is* possible the mac would create a ground loop where the pi doesn't, but not if your DAC has galvanic isolation as suggested by @somebodyelse . Even if there was a ground loop it would result in hum or other noise pickup. I guess under some circumstances this could "muddy" the sound.

I second the suggestion to put the Pi next to the Dac on WIFI.
 

Jinjuku

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Thanks for your help here.
My first goal is complete galvanic isolation from the Pi.
Second is to reduce cable runs across the lounge room and keep the wife happy.
Thirdly reduce ground loops, and forth stop floating power supplies from adding 110v to my data stream.
Its not really the cpu load, its the noise of more processes running that aren't essential for playing music.
I have an excellent Imac running HQ Player or Pure music. It also is doing gazillions of other things that muddy the music output. My Pi4 LMS server and separate Pi4 Pi core player deliver a much cleaner signal to my Pontus 2 Dac than the IMac ever did.

Simplistically I am looking for a USB Bridge where each end is powered from it's USB port. The two dongles are paired and are not part of a mass of data traffic and noise on my router.
What can you recommend?

You already have galvanic isolation with a properly designed DAC

Connect the Pi via wifi and use a short USB connection to the DAC

Wifi may help with your ground loop

processes running equating to noise is a fallacy.

I have to ask: Given your post why are you running a Pi and not a Sonore? You seem convinced of the many shortcomings of the Pi as an endpoint.
 

reprap

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Thanks for your interest and ideas on my quest. Having worked through the "why"
I need help on the "how" to achieve my goal.I am looking for a usb powered wifi dongle to act as a bridge between my Pi player and my USB Dac. I prefer not to use the Pi internal wifi for reasons some of you have mentioned.
The USB cable connector casings are electrically connected together thereby joining the DAC to the Pi or IMac if so cabled.
What can you recommend?
 

Jinjuku

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Thanks for your interest and ideas on my quest. Having worked through the "why"
I need help on the "how" to achieve my goal.I am looking for a usb powered wifi dongle to act as a bridge between my Pi player and my USB Dac. I prefer not to use the Pi internal wifi for reasons some of you have mentioned.
The USB cable connector casings are electrically connected together thereby joining the DAC to the Pi or IMac if so cabled.
What can you recommend?

What problem are you trying to solve? Ground loop hum? Some perceived fidelity shortcoming with the Pi?
 

reprap

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You already have galvanic isolation with a properly designed DAC

Connect the Pi via wifi and use a short USB connection to the DAC

Wifi may help with your ground loop

processes running equating to noise is a fallacy.

I have to ask: Given your post why are you running a Pi and not a Sonore? You seem convinced of the many shortcomings of the Pi as an endpoint.
The Sonore is way out of my budget range. I am simply looking for a wifi solution with minimum other traffic while avoiding yet another switch mode power supply to run it.
Any recommendations?
 
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