Terminate unused digital output?

Chester01 · Apr 18, 2006, 07:01 PM

I have heard that terminating an unused spdif/digital out will provide better sound quality; See:
http://www.audioasylum.com/audio/twe...ages/1571.html
It mentions a 75 ohm resistor being used for SPDIF; should this be done on the audigy/audigy 2? Would you expect to see any benefit in output quality? I am unsure that this would have an effect; if TravelRec or someone more knowledgeable in the electronics side of the card has any info please let me know. Thanks!

JohnN · Apr 19, 2006, 08:43 AM

I wasn't convinced at first but I had a quick Google over lunch.

Terminating a digital line with it's characteristic impedance (75Ohm in this case) is a physical truth. It will prevent reflections back into the SB SPDIF.

But what affect that would have is unclear to me. Also, I wager that you'd need equipment better than your ears to detect it.

One thing he suggested was that the refelction could cause jitter.
I failed to find the typical speed of the SPDIF, but I guess at something in the order of 2MHz??? (44.1k x 2 x 24bit???). Who thinks they could detect a few UI's of jitter at 2MHz?

One link points out that a SPDIF receiver will include the termination, so, yes, the system does need it when in use.
I am not yet, however, convinced that you would detect an improvement by just terminating an UNUSED output.

[ Foot say hello to mouth.... :-) ]

BR
JN

Chester01 · Apr 19, 2006, 06:30 PM

i tried it; it pretty much sounds the same to me... I suppose its nice to know that i have better quality now though... :-/

TravelRec. · Apr 21, 2006, 11:40 AM

I think this is completely useless! If the digital drivers are driving nothing, they produce less EMI than if they drive a low impedance resistor. If you connect this resistor, the digital output has to source current all the time, this can´t be better than not to connect it - my opinion. If you connect digital coaxial cables with other devices, the terminating resistor is inside the receiving devices. BTW: the card is designed that no (significant) digital noise can bleed into the analog output stages, so what...

Chester01 · Apr 21, 2006, 04:50 PM

Thank you for your advice TravelRec

TravelRec. · Apr 22, 2006, 01:17 PM

No problem

Apr 18, 2006, 07:01 PM	#1
Chester01 DriverHeaven Senior Member Join Date: Jan 2004 Location: St. Cloud, MN Posts: 487 Rep Power: 0	Terminate unused digital output? I have heard that terminating an unused spdif/digital out will provide better sound quality; See: http://www.audioasylum.com/audio/twe...ages/1571.html It mentions a 75 ohm resistor being used for SPDIF; should this be done on the audigy/audigy 2? Would you expect to see any benefit in output quality? I am unsure that this would have an effect; if TravelRec or someone more knowledgeable in the electronics side of the card has any info please let me know. Thanks! __________________ COMP: Dual Intel PIII 733 Mhz; GeForce 4 Ti 4600; 1.128 Gb RAM; SB0350 (Audigy 2 ZS Platnium) STEREO(I UPGRADED):Crown Audio K1 and K2 amplifiers (4000 watts at .1% THD ), JL 13w7 Subwoofer (6.5 CF) (2) 18" PR's, Klipsch SB-1's, some cement blocks for speaker stands...

Apr 19, 2006, 08:43 AM	#2
JohnN DriverHeaven Junior Member Join Date: Mar 2006 Location: Notts, UK Posts: 68 Rep Power: 0	I wasn't convinced at first but I had a quick Google over lunch. Terminating a digital line with it's characteristic impedance (75Ohm in this case) is a physical truth. It will prevent reflections back into the SB SPDIF. But what affect that would have is unclear to me. Also, I wager that you'd need equipment better than your ears to detect it. One thing he suggested was that the refelction could cause jitter. I failed to find the typical speed of the SPDIF, but I guess at something in the order of 2MHz??? (44.1k x 2 x 24bit???). Who thinks they could detect a few UI's of jitter at 2MHz? One link points out that a SPDIF receiver will include the termination, so, yes, the system does need it when in use. I am not yet, however, convinced that you would detect an improvement by just terminating an UNUSED output. [ Foot say hello to mouth.... :-) ] BR JN __________________ AMD 64 skt 939 4000+, 2G DDR, XFX6800GT, 80G + 200G, Audigy2 Value, IKEA room

Apr 19, 2006, 06:30 PM	#3
Chester01 DriverHeaven Senior Member Join Date: Jan 2004 Location: St. Cloud, MN Posts: 487 Rep Power: 0	i tried it; it pretty much sounds the same to me... I suppose its nice to know that i have better quality now though... :-/ __________________ COMP: Dual Intel PIII 733 Mhz; GeForce 4 Ti 4600; 1.128 Gb RAM; SB0350 (Audigy 2 ZS Platnium) STEREO(I UPGRADED):Crown Audio K1 and K2 amplifiers (4000 watts at .1% THD ), JL 13w7 Subwoofer (6.5 CF) (2) 18" PR's, Klipsch SB-1's, some cement blocks for speaker stands...

Apr 21, 2006, 11:40 AM	#4
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,704 Rep Power: 42	I think this is completely useless! If the digital drivers are driving nothing, they produce less EMI than if they drive a low impedance resistor. If you connect this resistor, the digital output has to source current all the time, this can´t be better than not to connect it - my opinion. If you connect digital coaxial cables with other devices, the terminating resistor is inside the receiving devices. BTW: the card is designed that no (significant) digital noise can bleed into the analog output stages, so what... __________________ Always take a look behind.

Apr 21, 2006, 04:50 PM	#5
Chester01 DriverHeaven Senior Member Join Date: Jan 2004 Location: St. Cloud, MN Posts: 487 Rep Power: 0	Thank you for your advice TravelRec __________________ COMP: Dual Intel PIII 733 Mhz; GeForce 4 Ti 4600; 1.128 Gb RAM; SB0350 (Audigy 2 ZS Platnium) STEREO(I UPGRADED):Crown Audio K1 and K2 amplifiers (4000 watts at .1% THD ), JL 13w7 Subwoofer (6.5 CF) (2) 18" PR's, Klipsch SB-1's, some cement blocks for speaker stands...

Apr 22, 2006, 01:17 PM	#6
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,704 Rep Power: 42	No problem __________________ Always take a look behind.