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Tuesday, January 1, 2013

High Pitched Audio QRM in SS #148

Two listeners blessed with good high frequency hearing alerted me to the fact that the latest podcast had some annoying high pitched noise in the background.   Peter, VK2TPM was the first to report it -- he sent along the above spectral analysis of a gap between words.  Steve,  W1KF,  also heard it, and provided a clue that I think solved the mystery.  

Steve noted that the noise was not present during the sponsor ads that were included in this episode. 
That let me figure it out.   On Saturday when I was recording this,  I got through about half the show when the power went out (that happens a lot here).  The battery in the laptop I was using to record the podcast saved the day and no data was lost.  The power came back on within a few minutes, but the outage had turned off the main PC in the shack.  That PC (AND ITS FAN) remained off when I was recording the ads.   I did the same kind of noise removal processing that I always do, but this time the noise sample that I used was taken from the mic with the main PC (AND ITS FAN) turned off.  My guess is that the whine from the fan (which I can't hear due to tinnitus) didn't make it into the noise sample, and thus didn't get removed from the podcast audio.    I went back and did a couple of rounds of noise removal and low pass filtering.  I think (I HOPE) I got rid of the offending noise. 
I have uploaded a new and hopefully improved version of the podcasts.  Audio reports will be appreciated.   

One of my New Years resolutions is to improve the technical and substantive quality of the podcast. 

Thanks Peter, Thanks Steve. 

Happy New Year to all! 
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20


  1. My hearing is inline with my age as I didn't suffer the high pitch noise leaving me to just enjoy it - thank you.

    Concerning 'who is Dan' from Dan's small parts - how about inviting him onto your next podcast via Skype or something to tell us his story???

    Have a good one over there



  2. Sounds good to me...but then, I was listening to Led Zeppelin whilst repairing the PA on one of my QRP jobs before I listend to SS. !Happy New Year! (Y que sea próspero y pacífico,t ambién)

  3. Hi Bill,
    Another great podcast. I also noticed the high pitched noise on the last couple of podcasts. To me it sounded like the squeaking of a cassette tape (lol), but my ears are not as good as they used to be either (thanks to my Navy days around jet aircraft). I was thinking that looking at your podcast with some software would help in troubleshooting. Other user's came to the rescue. I hope you and your family have a safe and prosperous New Year!


  4. I have to go along with Al. When I'm not listening to Soldersmoke, I'm blasting Urge Overkill, Motorhead, and Old Crow Medicine Show--and like you, Bill, I've got tinnitus (a sharp notch at 5K, they say). My listening setup is: Samsung Galaxy S3>Podcast Addict app>Bluetooth to Boss Audio 758DBI Media Receiver. The upper frequency limits of your MP3 encoding scheme might help to repair this--or better yet, just apply a low-pass filter, because those crickets (actually the pesky sound I've heard on 146 and 147--specifically stopping on 146 when you take a break, then gradually coming in by the mailbag) are quite loud in my listening setup. Loudest would be the first half of 146.

    I don't think it's an acoustic source in the shack. It sounds to me like electrical interference from some other component in your roadkill PC setup, because it reaches a gradual crescendo and threatens at times to swallow you up, when you speak slightly off-mic. It's also not a pure sine wave, because as I've heard (and the spectrum analysis submitted above indicates) there's at least one harmonic in there to make it that much harder to pin down or filter out.

    Are you using a USB mic or just a mic plugged into your soundcard? Try this simple test--if you have an Android phone in the house, download Tape-a-Talk, a free app, and record your voice in your shack. If you hear it there, then you'll know at least if it's present acoustically in the shack. Otherwise, it's being caused by your setup itself.

    All this blather aside--I love the podcast, and it keeps me rollin' on my 50-mile commute to and from Buffalo, MN every day. Thanks!

    Jonathan KC7FYS


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