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Buffalo DAC (ESS Sabre 9008)

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#1,481
Russ White said:
2) DSD mode does not utilize the custom FIR filters. So if you are thinking of using the ES9018 to do an active filter DSD input is not an option.
Click to expand...

Interesting bit of info here! So the ES9018 supports user downloadable FIR filter coefficients? Are the coefficient sets independent for each channel? How many taps are possible per channel?

Best regards,
A curious prospective TwistedPear customer who would like to use the Buffalo for a stereo 4-way active XO, and therefore would like board #2 🙂
 
#1,482
ojg said:


1) Interesting bit of info here! So the ES9018 supports user downloadable FIR filter coefficients?

2) Are the coefficient sets independent for each channel?

3) How many taps are possible per channel?

Best regards,
A curious prospective TwistedPear customer who would like to use the Buffalo for a stereo 4-way active XO, and therefore would like board #2 🙂
Click to expand...

1) Yes.
2) Yes.
3) I can't say at the moment, not because I don't know, but I will tell you the filter operates in two modes. Dustin has promised an app note for people wishing to implement an active filter. I will let him speak to that. I don't want to get it wrong in any case. 🙂 I am still new to the DSP aspects.

Cheers!
Russ
 
#1,484
Well, let me correct myself. That's a provisional yay...

Whether the ES9018 will be usable as a speaker crossover engine is dependent on the number of FIR taps available.

To illustrate this let's use a 4th order Linkwitz-Riley filter as an example. To approximate a 4th order LR lowpass at 2000Hz with a FIR filter running at Fs=96kHz you need approximately 128 taps.
A 4th order LR lowpass at 300Hz will need ~512 taps.
A 4th order LR lowpass at 60Hz will need ~2048 taps.

So depending on the number of taps available this chip may or may not be usable as a digital crossover for other than mid/tweeter crossovers. If that is the case then much of the market for a type #2 board disappears don't you think? Then it would only be interesting for multichannel surround sound applications.

A bit of reverse engineering applied to page 18 of the ES9008 datasheet indicates to me that it has a 128 tap half-band FIR filter. Am I close?
 
#1,485
ojg said:
Well, let me correct myself. That's a provisional yay...

Whether the ES9018 will be usable as a speaker crossover engine is dependent on the number of FIR taps available.

A bit of reverse engineering applied to page 18 of the ES9008 datasheet indicates to me that it has a 128 tap half-band FIR filter. Am I close?
Click to expand...

I will see if I can get you more information, but here is what I know:

There are two filter mode to which you can apply custom coefficients:

1) Slow roll-off which allows 64taps. The first is always 0.

2) fast roll-off which employs an interpolated filter at 2x and 4x making it an 8x oversampling filter.

The best thing I can suggest for now is to read up on interpolated filters:

http://www.mathworks.com/access/hel...m=0&ct=result&cd=1&q=interpolated+FIR&spell=1

To be honest I don't know enough on the subject yet to say how well it will work as an active filter, but I do know that ESS plans to incorporate that application in their demo board UI.

Cheers!
Russ
 
#1,487
Hmm, that's what I feared. The custom FIR filters are not meant for crossover use but are meant for those who wish to design their own upsampling filters. That way ESS can compete well with the Wolfson DACs and their choice of upsampling filters.

Going to 3rd, 2nd or 1st order filters do not reduce the requirements for number of filter taps very much. In this case it's the ratio of sampling frequency to crossover frequency that is the major factor. The higher this ratio the more taps you need.
 
#1,488
ojg said:
Hmm, that's what I feared. The custom FIR filters are not meant for crossover use but are meant for those who wish to design their own upsampling filters. That way ESS can compete well with the Wolfson DACs and their choice of upsampling filters.

Going to 3rd, 2nd or 1st order filters do not reduce the requirements for number of filter taps very much. In this case it's the ratio of sampling frequency to crossover frequency that is the major factor. The higher this ratio the more taps you need.
Click to expand...
Right. Hence my original question (and the doubt in my voice at the time).

Ok. Back to finding another solution.

peter
 
#1,489
Use of custom coeffs as active filter.

I would not be surprised if it works at low freqs, or if it does not.

I have not looked at it close enough to judge yet.

I do know that Dustin seemed to be indicating the interpolated filter effectively solves the issue withe low number of taps. But I am completely out of my element here. The question is best posed to him and not me. 🙂

I do know, they plan on incorporating the featire in their GUI.

Cheers!
Russ
 
#1,492
Re: Buffala32 thoughts and design considerations

Russ White said:

Here is the skinny. We are planning two new boards.

1) A simple stereo (or mono if you use a controller) Buffalo replacement designed to work primarily in hardware mode while supporting I2C input for control options including Volumite and Femto. This board would only be able to support a single SPDIF and I2S stereo input because of the constraints of using the chip in hardware mode. The 4 differential DACs per side would be in parallel In Short DSD mode would not be available on this board because of the way the chip supports hardware mode. Its a design compromise in favor of simplicity and ease of use over complexity and flexibility.
Click to expand...

Board #1 for me.
Which is the ETA?
 
#1,498
mono playback

hi everybody.

i just finished my buffalo and it sounds great but no imaging.

i tried a test cd and i found that it plays mono.

both speakers work but they play the same things.

currently i am using the buffalo without output stage straight

to the preamp through a coupling cap and a resistor.

any ideas what can be the problem?

thanks in advance

george.
 
#1,499
Re: mono playback

back said:
hi everybody.

i just finished my buffalo and it sounds great but no imaging.

i tried a test cd and i found that it plays mono.

both speakers work but they play the same things.

currently i am using the buffalo without output stage straight

to the preamp through a coupling cap and a resistor.

any ideas what can be the problem?

thanks in advance

george.
Click to expand...

My best guess would be that you are using opposite phases and it sounds like mono.

You will not get stellar performance without a proper output stage (filtering), and certainly not if you are not utilizing the DAC's differential outputs.
 
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