Linux Audio the way to go!?

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col

col

Member
Joined 2008
minirig.org.au
Thought i would chime in on this discussion since i have quite a lot of experience with this. Ive been running a linux powered audio server/player for around 4-5 years now. In its current form, the audio path is: mplayer (FLAC sources) -> jack -> brutefir (does high/mid xovers & sub xover) -> jack -> Envy24HT (modded with 3 optial spdif outputs) -> 3x spdif fibre -> DIY amp (3 x optical spdif inputs to 6ch bridged gainclone amps, same PCBs for minimal noise) -> speakers I went with this setup due to my need for very sharp xovers req for my Seas magnesium drivers. BruteFIR is an awesome piece of software. It can do huge FFT's (=very high quality) with very little CPU usage and audio delay. With this setup i can tune the XO points perfectly, apply levels/EQ's to each separate speaker driver output (and overall), do room compensation, etc without ever having to touch any analog circuitry.
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MWT, that sounds like an awesome setup. can you describe how you are doing the Digital to Analogue conversion and what hardware/chips are involved there? My guess is that would be the system weakness?

col.
 
N

nyc_paramedic

Member
Joined 2008
phofman said:
I have been thinking about a networked linux audio player with minimum EMI/RFI, with quality output. The standard PC technology produces a lot of electrical noise.

Something like this:

* a very low power solution, e.g. Asus WL500G Premium
* 5V linear power supply, no SMPS (I know there is a step-down SMPS onboard but there is probably no way around and I could not find a linux-capable board without the step-down SMPS)
* debian http://wpkg.org/Running_Debian_on_ASUS_WL-500G_deluxe
* 24-bit MPD + alsa, long latency to keep CPU load at minimum

Now the sound part. The router has one miniPCI slot. I could not find any miniPCI quality sound card. But there is supposed to be a simple miniPCI to PCI adapter http://www.costronic.com/Ev09mp.htm, no idea about price. I would prefer the model with the short flat cable as it allows placing the PCI card (e.g. Juli, Onky etc.) to a separate shielded compartment. It would even allow powering the card with a separate linear power supply, the required soldering should be rather straightforward. Timing of the PCI circuits of the card is not critical (as long as the communication works), the audio part is clocked by a separate crystal.

Another adapter is at http://www.getcatalyst.com/adapter_moreInfo_pci2mini3-3.html costs 125USD, rather expensive for a PCB with two connectors.

I am aware the price would approach dedicated audio solutions (Squeezebox Duet, etc), OTOH the quality could be substantially higher.
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Phofman,

Would you consider the ALIX board I mentioned in a previous thread? I've been running MPD and have been *really* happy with the sound quality. I haven't touched my high end transport in months.

Specs:http://www.pcengines.ch/alix3d2.htm
Schematic in PDF: http://www.pcengines.ch/schema/alix3d.pdf

Board has 2 Mini-PCI slots and a LPC bus.
Very low power consumption.
x86 CPU, so compatible with most Linux OS without recompiling
Runs Debian based Voyage Linux from CF entirely in RAM.
And in regards to low latency, seems as if my kernel's time is set for 1000Hz. From
/boot/config-2.6.26-486-voyage:

CONFIG_SECCOMP=y
# CONFIG_HZ_100 is not set
# CONFIG_HZ_250 is not set
# CONFIG_HZ_300 is not set
CONFIG_HZ_1000=y
CONFIG_HZ=1000
CONFIG_SCHED_HRTICK=y
# CONFIG_KEXEC is not set
# CONFIG_CRASH_DUMP is not set


The board is relatively inexpensive at $125 USD.

And another (off the wall?) idea:

PC Engines does do custom boards in quantity. Would the group here be interested in coming up with suitable "audiophile" SBC design and doing a group purchase?

Adding IR receiver? Placing the USB port in the back and LED's in front? Coming up with a nicer enclosure? Other hardware design changes?
 
E

ejaouen

Member
Joined 2007
ponctey.fr
To my mind the best solution would be a simple small pc motherboard including a VIA envy24 or envy24HT soundcontroller (it outputs 4 I2S channel pair).
Is there a soundcard or motherboard including envy24 or envy24HT chip where it would be very easy to tap the I2s outputs ?
I would like to put a wavefront (alesis) OPTOGEN (ADAT encoder) chip directly on the envy I2s outputs.
I love the envy24 soundcontroller chip and it is perfectly ALSA recognised but I would like its I2s outputs bare (nothing after that) on a pcb which does not exist in the market.
 
M

MWP

Member
Joined 2002
col said:
MWP, that sounds like an awesome setup. can you describe how you are doing the Digital to Analogue conversion and what hardware/chips are involved there? My guess is that would be the system weakness?
Click to expand...

I used PCM1703 -> PCM1798 -> relay switched volume control -> 4 x OPA627 -> 4 x LM3876 .

There are 3 of these amp boards to output the req 6 channels.

An externally hosted image should be here but it was not working when we last tested it.
 
M

MWP

Member
Joined 2002
ejaouen said:
To my mind the best solution would be a simple small pc motherboard including a VIA envy24 or envy24HT soundcontroller (it outputs 4 I2S channel pair).
Is there a soundcard or motherboard including envy24 or envy24HT chip where it would be very easy to tap the I2s outputs ?
I would like to put a wavefront (alesis) OPTOGEN (ADAT encoder) chip directly on the envy I2s outputs.
I love the envy24 soundcontroller chip and it is perfectly ALSA recognised but I would like its I2s outputs bare (nothing after that) on a pcb which does not exist in the market.
Click to expand...

It was fiddly, but i did it myself.

An externally hosted image should be here but it was not working when we last tested it.
 
P

phofman

Member
Joined 2005
Hooking to I2S lines is a great way, congratulations. BTW this is exactly the case where I think that placing the PCI card remotely and shielding it from the noisy MB would bring sonical benefits.

Alix cards look very good too. Perhaps it is a question of which benefits they would bring compared to the router board. They have no VGA either (i.e. audio only), no PCI either (i.e. still needing the hard-to-get miniPCI-PCI adapter), CPU performance probably does not allow for brufir upsampling to DAC native conversion frequency either. They cost twice the router in my country and their level of EMMI/RMI will probably exceed the router board too.

But this was just my idea, there are many ways to go. Perhaps the Asus router performance would not suffice for decoding compress formats, such as flac. Perhaps the Alix performance would suffice for brutefir upsampling (which I find VERY important for the uncompromizing solution).
 
D

dwk123

Member
Joined 2002
Remember, the Delta 1010 pci card has a DB25 connector with all the I2S lines on it. If you can find a used 1010 unit with a malfunctioning external dock, it may be the easiest/cheapest way to try to do this.

I have never seen a motherboard with an Envy24, but I did very recently see one with the 'Via Vinyl' 1616ht(I think) chipset on it. Might even have been on an Epia, now that I think about it. I don't know whether this has the same basic architecture, though.
 
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ejaouen

Member
Joined 2007
ponctey.fr
Remember, the Delta 1010 pci card has a DB25 connector with all the I2S lines on it. If you can find a used 1010 unit with a malfunctioning external dock, it may be the easiest/cheapest way to try to do this.
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Yeah I have a delta1010 (superb value and quality but I want even better) and I know I could use its internal PCI card, it would be great.

My goal is to have isolation from the PC and better quality DACs with discrete output stages.
But I think it has LVDS tramitters on it just before the DB25 , isn't it ?
Do I need some kind of LVDS receiver before being able to use I2S lines to the OPTOGEN chip inputs ?
I would like ADAT only because of the optical isolation (from the pc ground) it offers.
But with I2S (LVDS converted ?) from the envy24 of the delta PCI card maybe I could forget ADAT conversion stage and simly use some isolators on the receiving side (my 8 channel 24bit 44100hz DAC).
What kind of isolator would suit this ?
Does anybody kow what kind of chip (line driver ?) is used just before the DB25 connector in delta 1010 PCI card ?

thank you in advance
 
UnixMan

UnixMan

Member
Joined 2005
audiofaidate.org
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