16x Digital interpolation filter - drive PCM56, PCM58, AD1865 and so on up to 768 kHz

[rWolverine]

Hi 3lite!
I would like to purchase one, PM sent!

 

[samoloko]

3lite,
I am Interested at filter
Is project still available

 

[Luke]

me too, come on 3lite make a batch for us

 

[samoloko]

I have seen positive review about 16 x digital filter working with pcm1704 on audiostereo pl forum. I don't know about other proven and simple solution to feed old R 2R dacs with clean signal. Just take AK4118 based front end - receiver an Interface, this filter and your favorite old R 2R dac.

 

[Luke]

dont you mean an AK4137 SRC?

 

[samoloko]

I mean AK4118 AK4118 Digital Receiver Board Audio Decoder DAC SPDIF to IIS Coaxial Optical USB AES EBU Input Support XMOS Amanero OLED| | - AliExpress

 

[abraxalito]

Something like this - AK4137 I2S/DSD?????? ??PCM/DSD?? ??DOP??-??? ?

 

[samoloko]

AK4137 I2S/DSD based pcb does not accept spdif
the pcb I point out does have lowest possible jitter reciever with RCA In, Optical In, AES In, USB In
I am almost sure that 16 x digital filter does not want to get processed upsampled Input

 

[weissi]

I'm not sure it has been posted already (most likely):

Digital Interpolation Filter (FIR) - KuSy Audio

 

[Luke]

Something like this - AK4137 I2S/DSD?????? ??PCM/DSD?? ??DOP??-??? ?

Hi Abraxalito, I struggle with this stuff. I am trying to fix NOS droop, high frequencies of my dac (TDA1541) are missing. My understanding is it can be fixed with either:

1/ upsampling with the board you posted, ie i2s out is a higher sampling frequency and that makes the droop much less. (I think its no longer a NOS dac, is this correct?)

2/ Digital filter which is this board the thread is about

3/ correct it with a analog filter. I'm not capable of designing/modifying filters etc.

Am I on the right track?

 

[MarcelvdG]

This thread is about a digital interpolation filter, also known as oversampling or upsampling filter, so both 1/ and 2/ would make it no longer a non-oversampling DAC. Abraxalito has lots of experience with 3/, by the way.

 

[Luke]

thanks Marcel, so the AK4137 board above gives me 1 and 2, I think I will try it.

 

[abraxalito]

Hi Abraxalito, I struggle with this stuff. I am trying to fix NOS droop, high frequencies of my dac (TDA1541) are missing.

I take it you're running your TDA1541 at 44.1kHz rate? In which case yes, you'll get 'NOS droop' leading to an attenuation around 3dB at 20kHz.

My understanding is it can be fixed with either:

1/ upsampling with the board you posted, ie i2s out is a higher sampling frequency and that makes the droop much less. (I think its no longer a NOS dac, is this correct?)

Yes - even 2X upsampling reduces the droop to under 1dB at 20kHz.

2/ Digital filter which is this board the thread is about

Yes - this thread's about an upsampling digital filter. You can still correct your NOS droop with a filter which doesn't do upsampling (i.e. still outputs at 44.1kHz). The filter can be a purely digital one (but then you lose some headroom) or it can be a hybrid analog-digital one (aka 'transversal filter').

3/ correct it with a analog filter. I'm not capable of designing/modifying filters etc.

Yes - the simplest I've found is a 2nd order low-pass with a cut-off above 20kHz and with a calculated amount of peaking which undoes the NOS droop.

 

[analog_sa]

I mean AK4118 AK4118 Digital Receiver Board Audio Decoder DAC SPDIF to IIS Coaxial Optical USB AES EBU Input Support XMOS Amanero OLED| | - AliExpress

The Chinese are charging 44€ for a $4 chip and a little board? Wow.

 

[abraxalito]

Maybe only to those beyond the 'Middle kingdom'. Inside, its only $20 : AK4118 ??? ?? ???IIS ??XMOS/Amanero USB OLED??-???

 

[analog_sa]

Yup, they have cornered the "lazy diyer" market where markups are as high as on factory made audio equipment.

 

[Luke]

I take it you're running your TDA1541 at 44.1kHz rate? In which case yes, you'll get 'NOS droop' leading to an attenuation around 3dB at 20kHz.

So if I listen to red book cd I get -3db at 20khz, if I listen to 96khz hires I get 0.8db at 20khz?

 

[abraxalito]

Yes those numbers look right to me (assuming you meant -0.8dB).

 

[Luke]

yes I meant -0.8, thanks. looks like I need more hardware. Do you think this will have an adverse impact on the NOS sound?

 

[abraxalito]

Rather hard to say without knowing particular implementation details. In general reports I've heard say that dynamics get reduced when running at higher rates but the degree of degradation does depend on the particular DAC chip and I/V stage. I prefer to run a DAC chip only as fast as necessary for effective image filtering and no faster. This means 2XOS in my implementations.