NO low pass filter?

jmar · 16th January 2006, 08:35 PM

Has anyone had any luck removing ALL of the audible digital noise
on a PCM2702/2902 chip without using a low pass passive or active filter?

Just with good construction technique and filtering? (Impossible?)

Mine is very low level....but it's there.

danb1974 · 17th January 2006, 06:22 PM

Why not use the manufacturer's recommended opa2353-based LPF?

jmar · 17th January 2006, 06:52 PM

Just wondering (for my own education)...if it's possible to live without it and whether the noise can, in fact, be made inaudible.

Like I say, the noise level I hear on my board is quite low and I probably will use the filter.

Just learning.

I don't have that much experience with digital audio.

It may be impossible? to remove it all?

borisov57 · 19th January 2006, 10:02 AM

I use it without filter and without output op amp( i use dc blocking capacitor).
This way it sounds best. I do not hear any noise.
This is true for 2702. 2902 not sounds that good.

good luck,

borisov57

janneman · 19th January 2006, 11:09 AM

Quote:

Originally posted by jmar
Has anyone had any luck removing ALL of the audible digital noise
on a PCM2702/2902 chip without using a low pass passive or active filter?

Just with good construction technique and filtering? (Impossible?)

Mine is very low level....but it's there.

This noise is part of the signal and results from the DA conversion itself. Therefor, no amount of shielding or sophisticated construction will decrease it.

Depending on the sample frequency, the noise may actually reside above the audio frequency and as such is not audible directly. But it may upset the amplifier it feeds and/or cause intermodulation and/or slew rate limiting: the amp will now get hi freq, hi speed signal components it was not designed for. Some will be relatively unaffected, some will audibly degrade. It really depends on your particular situation.
Using at least some form of filtering will protect you to some extend.

Jan Didden

SY · 19th January 2006, 11:37 AM

Without an antiimaging filter, do you end up with a correct analog reconstruction?

jmar · 19th January 2006, 12:02 PM

Ok...thanks Jan.

I thought it had been more noise coming from the USB connection.

I know when you disconnect the USB cable, it turns the chip off?
(SSPND?)

Maybe I'll toggle the SSPND pin with the USB cable disconnected and listen.

If it's all just the DAC....it's pretty low and I have to turn the amp up to it's maximum to hear it....you can hear a high frequency "switching squeal."

Hey, it's alot better than tape hiss and I'm old enough to compare the two.

Werner · 19th January 2006, 12:53 PM

Quote:

Originally posted by SY
Without an antiimaging filter, do you end up with a correct analog reconstruction?

Ask the question like this:

at a sample f above 40kHz, do we conceptually need anti-imaging
filtering?

16th January 2006, 08:35 PM	#1
jmar diyAudio Member Join Date: Jan 2004 Location: Indiana	NO low pass filter? Has anyone had any luck removing ALL of the audible digital noise on a PCM2702/2902 chip without using a low pass passive or active filter? Just with good construction technique and filtering? (Impossible?) Mine is very low level....but it's there.

19th January 2006, 11:37 AM	#6
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Without an antiimaging filter, do you end up with a correct analog reconstruction? __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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17th January 2006, 06:22 PM	#2
danb1974 diyAudio Member Join Date: Jul 2005 Location: Timisoara	Why not use the manufacturer's recommended opa2353-based LPF?

17th January 2006, 06:52 PM	#3
jmar diyAudio Member Join Date: Jan 2004 Location: Indiana	Just wondering (for my own education)...if it's possible to live without it and whether the noise can, in fact, be made inaudible. Like I say, the noise level I hear on my board is quite low and I probably will use the filter. Just learning. I don't have that much experience with digital audio. It may be impossible? to remove it all?

19th January 2006, 10:02 AM	#4
borisov57 diyAudio Member Join Date: Feb 2002	I use it without filter and without output op amp( i use dc blocking capacitor). This way it sounds best. I do not hear any noise. This is true for 2702. 2902 not sounds that good. good luck, borisov57

19th January 2006, 12:02 PM	#7
jmar diyAudio Member Join Date: Jan 2004 Location: Indiana	Ok...thanks Jan. I thought it had been more noise coming from the USB connection. I know when you disconnect the USB cable, it turns the chip off? (SSPND?) Maybe I'll toggle the SSPND pin with the USB cable disconnected and listen. If it's all just the DAC....it's pretty low and I have to turn the amp up to it's maximum to hear it....you can hear a high frequency "switching squeal." Hey, it's alot better than tape hiss and I'm old enough to compare the two.

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