Signal A-B-Switching

Hello, i have a question on signal-switching!

A friend of mine wants to switch between 2 pcs of HD24 Recorders playing back the same Audiotracks in case one off them fails. He wants a big "emergency-knob" on the Front as this is for a Live-Show.
I am thinking about using jeffs relay plugin-boards for this task since there is a driver onboard and for convinience.

What i dont know if i need some kind of termination to be "click-free"?? I have testet one A-B Switch without any termination and the clicks were nearly not audible. If this will be the same with the HD24´s it will be fine but i am not sure about that.

Does anybody have any recommendations?? would be highly apriciated!!!!!

I have attached a schematic how i want to realize the switching  with relays ( Panasoniq TQ2 Relay).

Thanks for comments,
Wolfgang

Du meinst so etwas ?

I have only relays (and a transformer) in the audio path, nothing terminated.
no audible clicks (except on the click channel for the drummer  )

At the moment I'm working on the 3rd one for the 2013 tour,
if you want contact me and I can order some more PCBs.

Nice Builds!!!!!!!!

Thanks for reply, sent a PM!

regards,
Wolfgang

A simple switch will click, if it interrupts any audio signal in the middle of a waveform.

Advanced switching topologies generally deal with avoiding clicks (from DC) when no signal is playing.

JR

PS: There are methods to mitigate clicks from switching while music is playing but that is generally not considered worth the effort.

A simple switch will click, if it interrupts any audio signal in the middle of a waveform.

Advanced switching topologies generally deal with avoiding clicks (from DC) when no signal is playing.

JR

PS: There are methods to mitigate clicks from switching while music is playing but that is generally not considered worth the effort.

Click to expand...

Yes. I was thinking about DC. When the Mackie or Alesis HD24 (i dont know) has no DC on the outputs i will be fine. if there is dc.........
Thought about adding a Capacitor with Resistor to Ground on every input-leg. but it eats up space and i dont know if it is worth the cost.
If one of the playbacks has an error there will be an short interruption anyway so maybe i should not worry to much for clicks at -40dB.

at JR: What do you mean with "advanced switching technologies" ? Are you thinking FET-switching or something else?

regards,
Wolfgang

wolfgang said:

at JR: What do you mean with "advanced switching technologies" ? Are you thinking FET-switching or something else?

regards,
Wolfgang

Click to expand...

At least two...  Using high speed electronic switches you can sense for zero crossings and switch synchronously with the zero crossing to reduce click energy. This strategy is used in some digitally controlled mic preamps to de-click gain switching noise.  Another strategy is to apply HF pre-emphasis ahead of the switch, with complementary de-emphasis (HF roll-off) after the switch. This way the audio path sees a flat frequency response, but the click sees only the LPF.

I have used both technologies effectively in different contexts.  The pre/de-emphasis is not free, as you trade off head room which is reduced by the amount of HF boost, but I used this effectively in a cheap FET based noise gate years ago, that could switch quickly without the nasty artifacts or certainly reduced click energy.

Neither approach is worth the complexity for simple path switching.

JR

Thanks for your insight JR !

Your approach is for far more delicate switching utilities!

regards,
Wolfgang

In rehearsals we often switch between A and B, in the middle of songs etc.
Nobody noticed yet, not the musicians, not the FOH guys, even the light and pyro systems don't realise (switched LTC ...).

However, if you are in the need to hit the "panic button" in the middle of the show a small audible click will be the smallest problem to deal with 

Wolfgang, I will answer your pm later