Effect of wired digital inputs not in use

I use the 2 wired digital inputs on my DS (RCA & XLR) for a DAB tuner and an Airplay input (with adaptors to convert the optical digital output from an Apple TV to XLR). The Airplay input (XLR) is permanently active to allow immediate streaming from phones, iPad etc but I only switch the DAB tuner on when I wish to listen to the radio.

A couple of days ago while streaming music through the Bridge I noticed I’d forgotten to switch off the tuner. When I did I noticed an improvement in SQ - not massive just slightly clearer sound.

I remember years ago when dealing with multiple analogue inputs to a preamp it was advised to leave other sources ‘live’ and short the inputs to any unused inputs. The suggestion (fact?) was that open-circuit and unterminated inputs could act as aerials and thus feed RF signals into the preamp so increasing the noise in the preamp.

Could there be a similar effect with the wired digital inputs to the DS?

Any thoughts?

Well, everything matters and I wouldn’t dispute that you hear a difference. I suspect that unplugging the unused input would make a bigger difference, but that’s not really practical. I don’t think that it’s a question of unused digital inputs acting like an antenna. I think it’s more that changing the switching noises a little in the FPGA by processing different signals may change the color of the sound in minute ways. Whether that change is good or bad may depend more on the individual systems.

I would think the antenna theory only count if the input is high impedance?

Further developments …

I’ve been working my way through some downloads I bought from the Gimell download site (which currently has a 40% discount offer as it’s closing next week). One of the inputs I use on the DS is Toslink optical SPDIF from our TV. I have always made a point of switching off the TV before any serious listening, thinking I’d remove any related interference. Today I noticed that the sound of the Tallis Scholars singing works by Mouton was improved (more ambience, better imaging of voices) compared with what I’d heard yesterday. Then I noticed that today I’d forgotten to switch off the TV (from stand-by mode). So I guess that if there are multiple inputs connected to the DS then the best SQ is obtained when all those connected inputs are ‘live’!

Further developments …

I guess with hindsight this one is obvious but it was a salutary lesson for me that others might benefit from:

I use a Panasonic Hard-disk recorder to record TV and radio programmes we receive via TV in the UK; it is connected to the TV by HDMI. I normally leave the disk recorder in standby power mode but today I had left this machine fully powered up. With the TV in standby power mode, when I switched the disk recorder to standby power the SQ improved! Again more ambience and better imaging.

I guess it is possible that the video signal going from the disk recorder via HDMI to the TV (in standby power mode) might affect the Toslink output from the TV but this seems very unlikely. I suspect the improved SQ was due to my having switched off all the digital video processing hardware in the disk recorder, and hence any associated RFI.