How to avoid headphone damage from pulsed signals?

[angelonc]

I study auditory perception for work, so when I design sound files to be played during experiments, the first channel typically contains audio, while the second channel contains a sync pulse, which is basically a series of square pulses occurring at desired times during the audio.

My issue is that when I design these stimuli, they're saved as .wav files, and are automatically loaded to iTune's library. Sometimes they are accidentally played from my iTunes library, and it seems like the sync pulse in the second channel is really good at destroying the right speaker/earphone/whatever is playing that channel at the time. This makes sense... as going from 0 to relatively high voltage instantly will not be tolerated well by most speakers.

My question is, is there hardware that can prevent damage from this type of signal; some sort of conditioning amplifier? If so, any suggestions?

(I know the answer will ultimately be: "avoid playing bad signals through your headphones", but I am sincerely curious if there's some way to filter the signal to avoid damage)

 

[Chip Chester]

Can you modify or adjust the equipment you use during experiments? If so, greatly decrease the level of the sync pulses in the file, and amplify them back up by increasing the gain of the sync detection channel in your experimental apparatus. That way, as long as normal audio files are played at reasonable listening levels, the accidental playout of the perception files won't kill whatever you're listening on, or with.

Hardware-wise, nothing you put in one channel of everything you listen with will leave other signals untouched. So the hardware needs to go on your experimental apparatus.

I'm assuming these are on your phone because you play them from your phone into the apparatus? If that is not the case, and they're there by 'accident', put them in a separate folder, on a thumb drive, or somewhere iTunes doesn't think it can sync them to your phone.

If you have complete control over how your experimental apparatus works, you could use an initial timing pulse to map your sync, or lower-level actual SMPTE timecode to coordinate whatever needs synced. Many ways to make that stuff happen -- even sub-audible cue tones within the audio itself.

 

[cpt_paranoia]

My issue is that when I design these stimuli, they're saved as .wav files, and are automatically loaded to iTune's library

Can you not tell iTunes not to include files in certain directories? Or positively tell iTunes where to look?

I can't think of a media manager/player I have used that will not allow you to do this. I suppose the Apple "you don't need to worry about complicated things like where files are; just let us sort if out" approach may not support this sort of user control.

https://superuser.com/questions/106...-from-itunes-after-it-was-automatically-added

 

[BinaryMike]

I used to do precisely the same thing, but for tape recorder sweep frequency response measurement. I built a patch panel for the workbench that can selectively put the sync pulse on any one of four output channels and then route it to the scope sync input from any one of four input channels. I think Chip's advice to greatly reduce the level of the sync pulse is on-point here. There's no reason to blast the sync channel with maximum amplitude pulses. This is high-fidelity equipment, and it's fully capable of reproducing low-level sync pulses with clean enough shape for accurate timing recovery.

 

[Bob]

run it through audacity and lower the gain on the pulse channel.

 

[HTWillie]

What's the purpose of the sync pulse, and does it need to be so loud? Generate lower amplitude pulses. If you want to go the hardware route, a Limiter is the customary tool for the job, but I've no real experience with these.