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Creating pulsating sound before implementing in hardware

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mik3ca

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Based on my findings on another thread, it turns out one way I can have loud music and transmitter functioning on the same board (without the transmitter causing the sound to oscillate) at once is to have the board run one thing at a time.

This means I'll need to make pulsating sound in the hardware, but before I do that, is there some software out there that can automatically modify a generic sound file (like a wave file) so that I can define the same silence at specific intervals? For example, maybe play audio for 1 second then silent for 1ms then play again for 1 second then silent for 1ms etc.

I know I could use a standard audio file editor but thats a pain as I'll have to manually add breaks in to all sounds and that manual time is tedious especially when lining the silent points up correctly.

I just want to try the software that anyone can recommend to see how the sound is and if it is acceptable then I'll do it the pulse way and have my problems solved. Otherwise, I might have to lower volume because I tried other methods in my project to reduce interference without success.
 

ChrisP58

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I have a few thoughts, but want to understand the problem better first.

When you start a new thread that references another thread, and information in that thread may be useful to the new thread, it would be very helpful to include a link to the other thread.
 

mik3ca

Member
Yes pommie got the link correct. But I want to avoid turning the volume down so I want to see if following audioguru's idea of not transmitting and playing nearby audio at the same time works, which means I'll have to find software that can simulate chopped up sound to see if it sounds ok and if it does then I could do it on my micro or maybe even use a bilateral switch or something to turn the speakers off while transmission happens?
 

audioguru

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"Turning the speakers off" is the same thing as "muting" which is the same thing as "turning down the volume". Since I think the input of the audio amplifier is overloaded by the nearby radio transmitter then the audio amplifier input should be shorted to ground during transmitting. If audio is abruptly muted then it frequently causes a POP sound. Then ramping down the audio prevents the POP.
 

alec_t

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is there some software out there that can automatically modify a generic sound file (like a wave file) so that I can define the same silence at specific intervals? For example, maybe play audio for 1 second then silent for 1ms then play again for 1 second then silent for 1ms etc.
Methinks you could do that with LTspice (freeware simulator from Linear Technology), which can accept a .wav file as a PWL input for a voltage source, chop it (softly), then output the result as a .wav file.

Edit:
Just tried and it works. I chopped a .wav 10S snippet using 1mS width mutes at 0.25 sec intervals. The chopping is audible in quiet passsages but not so noticeable in louder passages. Rename the attached file as a .wav by removing the .txt extension.
 

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audioguru

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A transistor can short the amplifier input to ground to mute the amplifier.
How do I remove the .txt extension?
 

audioguru

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I downloaded the .txt file and it is shown as a Notepad document already called "chopped.wav". How do I eliminate the Notepad type of document? I got Windows 10.
File associations do not let me delete Notepad file type, just to change it to open with a different program type. I changed it to open with Windows Media Player and it opens and plays. I do not hear the breaks in the music. Thanks for the help.
 

alec_t

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Here's the same 10S snippet chopped differently. The mutes are each 5mS duration at 0.5S intervals. The mute function is softer, with a fade-out over 0.5mS, 5mS of silence, then a fade-in over 0.5mS. Even with 5mS mutes I can't hear them.

Edit: Attached is the template for a LTspice simulation, if anyone wants to play.
 

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audioguru

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Your chopped up audio sounds much better than cell phone audio that is frequently very badly chopped up.
 

unclejed613

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i've been looking at your original thread, and you said your speaker wires were 4 inches long... at 915Mhz that's a little bit longer than 1/4 wavelength (which is 3.22 inches). you might try using shielded twister pair to go to the speakers, or find some way to relocate the transmitter further from the audio circuits. or, if it's feasible use speaker wires shorter than than 1/8 wavelength (that's only 1.6 inches). make sure your audio input cables are well shielded too. avoid wire lengths of 3.22 inches or multiples (especially odd multiples) of 1/4 wavelength. another alternative to moving the radio module away from the audio circuits, is use an antenna cable with the antenna further away from the boards, and a snap-on ferrite at the antenna end of the RF cable to eliminate RF on the outside of the cable.

another thing i noticed, looking at your PCB, it's also close to 3 inches in length.
 
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