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Holmz,
I use APL’s USB audio input for sending digital audio up to 192Khz/24bit over USB from my Raspberry Pi3 .
The RPi3 is placed in the trunk powered by a 12-5V DC-DC regulator . I have attached an SSD and a 128GB flash disc to it . I have installed Volumio which is a free Linux based operating system tuned exclusively for music playback. The RPi3 becomes a headless digital audio player which is controlled over Wi-Fi from my android mobile phone or my android Dashboard Multimedia System.
I would suggest for better quality to send direct digital audio to APL instead of going into your head unit’s digital in and then from its RCA output to APL, as like this you have one DA-AD conversion less . In case your APL does not have USB input there are SPDIF output piggyback boards in the market for Raspberry which you can use to send direct coax digital to APL.

For car, do you recommend the Rasberry Pi over the Volumio Mini86?

https://volumio.org/product/volumio-mini86/
 

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Discussion Starter #102
I'd go with an AppleTV (if you got an Apple phone or iPod) to feed the APL via wifi. Probably my next project.

A 7" touchscreen combined with a Raspberry Pi or something would be pretty cool as well. Digital audio is great for car audio in several ways...
 

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Good info above, thanks.

I haven't tried these myself, but from my research, if you will be using an add-on DAC/SPDIF output board with the Raspberry Pi3, I've read from guys who are using them in very Hi-End home systems that the available DAC/SPDIF output boards are "okay" but not great compared to their other stand-alone units (which of course are many times more expensive, so theirs that). :rolleyes:

But if you're going straight into the APL USB input, it's a non-issue.
 

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I'd go with an AppleTV (if you got an Apple phone or iPod) to feed the APL via wifi. Probably my next project.

A 7" touchscreen combined with a Raspberry Pi or something would be pretty cool as well. Digital audio is great for car audio in several ways...

Yes, I have all Apple stuff and would certainly prefer to stay within their ecosystem, but do you think AirPlay is robust enough for in-car use? I sometimes have issues with it in my house, and my Apple TV is hardwired via ethernet to my router.
 

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Air play is wireless streming which may degrade the signal. Same with bluetooth.

I have been using use home media players with digital optical out since a decade for direct digital signal to DSP. I have used them to bitstream multichannel signals also...dts- dobly 5.1 in car.

Now I have Popcorn Hour A500. It has both optical and coaxial out. I think both optical and coaxial work simultaneously. I control it with an app on my android phone. You don't need a screen for display. Files can be browsed over phone and played. Works fine. Boot time is around 30-45 seconds.

Cons: I have to turn on my phone's wifi hotspot every time I sit in the car. IOS app not available.









Sent from my SM-G950F using Tapatalk
 

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Discussion Starter #106
Airplay is not compressing audio, it's WiFi:

What is the audio quality for this type of transmission?
In contrast to Bluetooth connections, which sometimes lead to downsampling and loss of quality, AirPlay is transmitting “CD quality” audio (16bit / 44.1kHz). This can easily be verified with the Audio Midi Setup tool that is located in the Utilities folder in your app directory.

For streaming content Apple is using the in-house Apple Lossless Audio Codec (ALAC). Here data density is permitted for up to 120 megabit per second. No matter what format the audio originally coded, your Mac or iOS gadget will turn it into a lossless audio stream. Only so-called “Hi-Res” Audio formats used by pros and audiophiles with higher resolution (e.g. 24 Bit / 192kHz) will be down-sampled to 16 Bit / 44.1kHz.
 

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Discussion Starter #107
Yes, I have all Apple stuff and would certainly prefer to stay within their ecosystem, but do you think AirPlay is robust enough for in-car use? I sometimes have issues with it in my house, and my Apple TV is hardwired via ethernet to my router.
No idea, no experience with the Airplay. It looks a little bulky judging from the pictures.
 

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Let's say you have the APL1012, and you have tuned it.

You get in the car and decide that the time alignment is a little off and you want to adjust it. Can the delays be adjusted in real-time while listening to the system? Or is the process a trial and error situation where you enter different delay numbers, and then have to listen and see if they improve the tune?

That's one thing I like about the Helix, is I can sit and listen while adjusting delay groups.
 

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Discussion Starter #111
Let's say you have the APL1012, and you have tuned it.



You get in the car and decide that the time alignment is a little off and you want to adjust it. Can the delays be adjusted in real-time while listening to the system? Or is the process a trial and error situation where you enter different delay numbers, and then have to listen and see if they improve the tune?



That's one thing I like about the Helix, is I can sit and listen while adjusting delay groups.


You can set delays while the system is on like any other DSP. Gotta do it from C5 software though.
 

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For car, do you recommend the Rasberry Pi over the Volumio Mini86?
subterFUSE , for car i have tested Volumio on three platforms: Raspberry RPi3, Asus Tinkerboard and Sparky but not mini86 so i can not comment about it. These three platforms are compact and are powered with 5V. The solution offered by Volumio with their mini86 is much bulkier and needs 12V so it might be trickier to get constant voltage regulation from the car's battery. From my tests , I liked the sound of ASUS Tinkerboard better but it had problems working with my Helix DSP HEC HD Audio USB card(that i had back then) plus its processor produced much more heat and needed good cooling. Sparky has more pronounced bass but i consider the sound of the Rpi3 more balanced. However the most decisive factor was the extensive support the RPi3 platform has from millions of users and the number of applications and add-on boards that one can find. Another problem one has to tackle is how to safely shut down the platform of his choice. If the power is suddenly cut off from the battery when switching off engine this is not a safe shut down, it is like switching off your PC suddenly by pulling the plug and this eventually might corrupt the OS that is installed on the SD card.For RPi3 platform there are some UPS add on boards that once they detect power cut off they automatically switch to battery power and execute a shut down command for safe shut down . Last but not least RPi3 is the cheapest of them all.
 

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How is volume controlled when using the HD USB Input?
By using the volume pot that Raimonds sends with the APL unit . He dispatches the unit with four pots : volume, sub volume, balance and presets as well as a ribbon cable that connects all these pots to the APL unit.
 

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The player needs to work in a 4 wheel drive. So it needs to be a bit rugged.
Holmz, I have been having my RPi3 player for over a year in a sports car with stiff suspension and under very hot temperatures during the summer with over 50-55 Degrees Celcius inside my trunk and no external ventilation. I have not had any problem so i consider it rugged enough.
 

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Holmz,
I use APL’s USB audio input for sending digital audio up to 192Khz/24bit over USB from my Raspberry Pi3 .
The RPi3 is placed in the trunk powered by a 12-5V DC-DC regulator . I have attached an SSD and a 128GB flash disc to it . I have installed Volumio which is a free Linux based operating system tuned exclusively for music playback. The RPi3 becomes a headless digital audio player which is controlled over Wi-Fi from my android mobile phone or my android Dashboard Multimedia System.
I would suggest for better quality to send direct digital audio to APL instead of going into your head unit’s digital in and then from its RCA output to APL, as like this you have one DA-AD conversion less . In case your APL does not have USB input there are SPDIF output piggyback boards in the market for Raspberry which you can use to send direct coax digital to APL.
Ok thanks... I will see if that works with an iPad as the controller.
 

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I am about to order one of these.

Should I get the 48 kHz or 96 kHz model?


My source will be the Sony RSXGS9 head unit via analog RCA cables.
 

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I am about to order one of these.

Should I get the 48 kHz or 96 kHz model?


My source will be the Sony RSXGS9 head unit via analog RCA cables.
My reasoning for the 48kHz was:
1) I doubt I hear well up high
2) I doubt that the filter banks are long enough to work well for a subwoofer.

Of course searching for the truth would be best.
Raimonds should be the one to opine on the matter.
 

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So less taps at 96 kHz?

Is it half the taps?

4096 seems to be a bare minimum number of taps for any chance of EQ in the sub range. More would be better.
 

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So less taps at 96 kHz?

Is it half the taps?

4096 seems to be a bare minimum number of taps for any chance of EQ in the sub range. More would be better.
Same number of taps, so it is more like the bin's frequency width at 96k is twice as wide as the bin's width at 48k. (I would need to break out the book, but I a man pretty sure it is conceptually correct.)

The ideal (I think) would be to resample the sub channel to 1 or 2 k-samples/sec and then use 128 bins (or something on that order).

In any case I figured 48k was enough for me.
 

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So at 96 kHz you need 2 times as many taps for the same frequency resolution at 48 kHz?
 
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