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Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 KHz

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S

spikestabber

Member
Joined 2015
Dimdim said:
If you have connected the I2S coming from the Amanero to the isolated I2S input, you must connect the Amanero's GND to the ISO GND. Otherwise you will definitely lose the benefit of the isolators and most likely have a problematic I2S connection.

So, no pros and cons. Just right and wrong.
Click to expand...

A good hint is to test continuity between USB ground, chassis, and audio ground regularly to verify that the isolation is good. I only get ~0.x ohm when it's plugged in, a loop that goes from the dac ground and the computer's ground.
 
K

kin1111kin

Member
Joined 2017
Help my dac 1541

What is the specific item at D1? Thank you
 

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F

fedde

Member
Joined 2002
fedde.nu
TNT said:
I would now like to make some speaker EQ and, if possible, phase compensation for a pair of line source speakers I have built. Looking back in the thread I did have this question a long time ago:

"As crossover: the dam1021/dam1121 have the hardware with support for up to 15 IIR biquad filters per board. How to do it is an advanced DIY project, not something I will provide support for. Probably much easier using a DSP....

Is all the information/prerequisites described in the manual to really pull this off?"

I mean; I don't request a guide, just want to know Sören, if all the prerequisites is in the manual to do this. So I don't start this investigation and project in wain.

Some of this compensation I would like to do as as IIR, some as FIR... for FIR I suppose I just "modify" the existing filters to also do passband processing in addition to the D/A conversion brick-wall filter.

If anyone know of such a project, please add a pointer - thanks!!

//
Click to expand...

I would advise to look into:
FIR vs IIR filtering

There is a handy Biquad calculation spreadsheet on this page.

The filter text file describes the format. So implementing a few biquad filters should be straightforward.

@Soekris
What is the internal precision of the Biquad filters in bits? On PC side I use double floats, so I wonder what precision I would potentially lose when moving processing to Soekris DAC.
 
N

Nanekiu

Member
Joined 2016
F

fedde

Member
Joined 2002
fedde.nu
fedde said:
@Soekris
What is the internal precision of the Biquad filters in bits? On PC side I use double floats, so I wonder what precision I would potentially lose when moving processing to Soekris DAC.
Click to expand...

@Soekris: I have one question more: are the IIR filters before or after (DAC) volume control? I presume the chain is like below?

Data input -> FIR filters to 352/384k -> IIR filters -> Volume control -> Upsampling to 3 Mhz -> Resistor banks -> Output
 
TNT

TNT

Member
Joined 2003
Paid Member
fedde, thanks I get the biquad now I and managed to load some. I think :)

What I'm a bit puzzled over is how they are deployed...

-- type 1 = FIR1, 2 = FIR2, 16..30 = IIR, 30 = Deemphasis
-- IIR Coefficients is b0, b1, b2, a1, a2. a0 is assumed to be 1.0000

and for example:

dam1021,44100,8,16,5,0.8
16 IIR biquad 1

b0 = 0.9172257802529049
b1 = -1.792384354953564
...
dam1021,44100,8,17,5,0.8
17 IIR biquad 2

b0 = 0.8272257802529049
b1 = -1.392384354953564
...

would these always be active in addition to every other filter in the DAM?

And there are 14 free? 16...30 -1 deemp=14

But maybe only 13 because 29 is taken by DC-blocking filter?

//
 
Last edited:
analog_sa

analog_sa

Member
Joined 2002
Power supply question

Got late onboard thanks to a cheap gen1 board.

First of all many thanks to everyone who helped raise the sound of this project from the simply unacceptable to the nearly sublime. Yes, i did listen to the board prior to any mods and understand well a friend who was an early adopter and who sold his board screaming in horror within its first week :)

So, after fixing Vref with plenty of capacitance, new filter resistor values and the "superreg" transistor mod, the result is indeed quite pleasing. Removing the horror ceramic cap filter at output also helped.

So, here is the question: why not give the clock a separate regulator? The 3.3v gets shared between the clock and the micro and all that separates them is a flimsy RC filter. The 1R resistor makes the separation very easy. Of course i tried it and the change was substantial but not entirely an improvement, perhaps due to the regulator i had at hand.
 
F

fedde

Member
Joined 2002
fedde.nu
TNT said:
fedde, thanks I get the biquad now I and managed to load some. I think :)

What I'm a bit puzzled over is how they are deployed...

-- type 1 = FIR1, 2 = FIR2, 16..30 = IIR, 30 = Deemphasis
-- IIR Coefficients is b0, b1, b2, a1, a2. a0 is assumed to be 1.0000

and for example:

dam1021,44100,8,16,5,0.8
16 IIR biquad 1

b0 = 0.9172257802529049
b1 = -1.792384354953564
...
dam1021,44100,8,17,5,0.8
17 IIR biquad 2

b0 = 0.8272257802529049
b1 = -1.392384354953564
...

would these always be active in addition to every other filter in the DAM?

And there are 14 free? 16...30 -1 deemp=14

But maybe only 13 because 29 is taken by DC-blocking filter?

//
Click to expand...

You need to use 352800 and 384000 as frequencies. And i think the gain should be 1 instead of 0.8. There are 15 IIR filters x 2 frequencies. Of the 15, 1 is used for deemphasis and 1 for 2Hz HPF. So you have 13 or 14 filters depending whether you want to use the 2Hz filter. By the way, a1 and a2 need to be inverted, this is not clearly described in the manual.

For example, I tried the following filters today:
(disclaimer, I did not measure the end result yet, but they appear to be ok)

dam1021, 352800, 8, 16, 5, 1
16 IIR filter, 352800 Hz, type=Low-shelf, freq= 160 Hz, gain= 4.5 dB, bw= 1.0

1.0005235415067368
-1.9964576108688858
0.99594457141929293
1.9964597340585233
-0.99646598973639311

dam1021, 384000, 8, 16, 5, 1
16 IIR filter, 384000 Hz, type=Low-shelf, freq= 160 Hz, gain= 4.5 dB, bw= 1.0

1.0004809936353041
-1.9967455877718776
0.9962734602126061
1.9967473802169671
-0.99675266140282137
 
TNT

TNT

Member
Joined 2003
Paid Member
Well, apparently there is a bug where only one (1) of the biquads gets executed even if you add several. At least that has been reported and verified with measurements. And I have not seen any bug reports saying it's gone.

Do you understand why there can be no coefficients under the 44,1 filter "declaration"? Like:

-- FIR1 filters for 44.1K/48K Samplerate

dam1021,44100,8,1004,3999,6.4
04 Linear Phase FIR1, 44.1 Ksps, 21.3 Khz - 1 db, 21.9 Khz -130 db

-- empty --

dam1021,48000,8,4,3999,6.4
04 Linear Phase FIR1, 48 Ksps, 23.2 Khz - 1 db, 23.8 Khz -130 db

-0.0000000033388097391170944
-0.0000000034687681803499536
-0.0000000030983288729504413
-0.0000000022790511231834339
-0.0000000011264009224108422

//
 
F

fedde

Member
Joined 2002
fedde.nu
TNT said:
Well, apparently there is a bug where only one (1) of the biquads gets executed even if you add several. At least that has been reported and verified with measurements. And I have not seen any bug reports saying it's gone.

Do you understand why there can be no coefficients under the 44,1 filter "declaration"? Like:
Click to expand...

Well the post was from April 2015 and Paul already got a firmware patch. So it would surprise me if the fix would not be in the current firmware. I am pretty sure that I have six filters running currently. Sounds good to me.

Regarding your question of the FIR filter, this is a feature. The filter number is 1000+4, which means that filter 4 (as defined for 48 kHz) will be reused.

Fedde
 
Last edited:
TNT

TNT

Member
Joined 2003
Paid Member
Okey / good to hear that. I was so sure one needed to generate different filters for different fs I didn't even consider that. Anyways I took a chance and exchanged that present filter with one I generated with rePhase which contain my line source compensation - generating it for 352,8 it plays very well now :D

So eventually success!

//
 
F

fedde

Member
Joined 2002
fedde.nu
TNT said:
Aha.... How inverted? Please explain.
Click to expand...

I used confusing (or even wrong) terminology here. I meant that in a Biquad filter, a1 and a2 get a minus sign. E.g. see the direct form diagrams in:
Digital biquad filter - Wikipedia

The question is then whether the minus sign is implemented in the hardware/software that processes the IIR or in the programmed in a1/a2 coefficients. In my case, I think I needed to add a minus sign for a1 and a2 in my IIR filter definition compared to the excel sheet.

Fedde
 
F

fedde

Member
Joined 2002
fedde.nu
TNT said:
Okey / good to hear that. I was so sure one needed to generate different filters for different fs I didn't even consider that. Anyways I took a chance and exchanged that present filter with one I generated with rePhase which contain my line source compensation - generating it for 352,8 it plays very well now :D

So eventually success!

//
Click to expand...
I think it is still possible to program in different filters for 44.1 and 48 kHz, by changing the filter number from 1004 to 4.

Fedde
 
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