Tag Archives: TomL

Tom’s Recommendations: Earbuds and EQ Settings for Shortwave Listening

Many thanks to SWLing Post contributor, TomL, who shares the following guest post:

Earbuds for Shortwave Listening

by TomL

A few years ago I had bought the discontinued Sennheiser MM 50 earbuds for a cheap price on Amazon to use in my various radios.  The portable radios in particular can use more fidelity because of their small, raspy speakers.  I also like to listen without bothering others around me who might not want to listen.  And earbuds are a LOT more comfortable for my ear lobes than any over-the-ear headphones I have ever used.  Furthermore, the old Apple iPhone 4 earbuds were very harsh to listen to.  However, a trade-off is that, generally, earbuds are somewhat fragile; one of the two pairs of MM50’s died through mishandling.

I was generally happy with them while listening to Shortwave broadcasters with a mix of news/talk and music.  I especially liked them on Mediumwave listening; stations can sound surprisingly good when playing music.  Then I tried using these earbuds on my Amateur Radio transceiver, a Kenwood TS-590S.  I was impressed how clear they sounded with a lack of distortion, although there was too much bass.  Fortunately, Kenwood supplies USB connected software with an TX & RX 18 band EQ (300 Hz spacing, not octaves).

Here is a frequency response chart I found from Reviewed.com for this model:

One of the notable things about these earbuds is the total lack of distortion.  Most likely one of the reasons they sound so clear on Shortwave, which has many LOUD audio spikes.

I had not wanted to get Bluetooth earbuds.  However, I had recently upgraded my cell phone and NO headphone jacks anymore!  So, while I do not use Bluetooth yet for radios, I can see a time in the future to get a Bluetooth transmitter to plug into a radio with a headphone jack.  I am reluctant since I do not like having to recharge my earbuds and I put in a lot of radio listening time.  Am I supposed to buy two Bluetooth earbuds and swap while charging?  Maybe in the future.  And also, am I supposed to buy a Bluetooth transmitter for every non-Bluetooth radio I own?  Not likely gonna happen.

In the meantime, I ordered cheap wired earbuds from Amazon.  I had a $5 credit for trying Prime, so when I saw these Panasonic ErgoFit wired earbuds (RP-HJE120-K) for slightly over $10, I said to myself, “why not?”.   Supposedly wildly popular, they are one of the most rated products on all of Amazon with 133,821 ratings/opinions (perhaps Russian bots?!?!?).

Here is a frequency response chart from ThePhonograph.com for these Panasonic earbuds:

You can see comparatively that the bass response in the very good Sennheiser MM50’s is much stronger, being good music earbuds.  But for voice articulation, not as much, even though they have no distortion.  The Panasonic ErgoFit’s have more modest bass, less of a dip in the lower midrange audio frequencies, and more importantly, has a peak near 2500 Hz and its harmonic 5000 Hz.  The highest highs are also modest compared to the Sennheiser model.  This general frequency response to “recess” the bass and treble frequencies and peak the 2500 Hz is very useful for voice intelligibility.

As described by the famous speaker-microphone-sound-system maker, Bob Heil relates what he learned from the scientists at Bell Labs many years ago.  Speech intelligibility is enhanced when audio is compensated for our natural human hearing.  Equalizing below 160 Hz, reducing the 600-900 Hz region, and peaking the 2000-3000 region centered at 2500 Hz will increase intelligibility dramatically.  The story goes that Bell Labs was tasked by parent AT&T with finding out why the earliest phones in the 1920’s sounded so muffled and hard to understand.  After many experiments, the scientists found the most important frequencies for our ears + brain to comprehend speech.  In other words, our ears are not “EQ-flat” like a scientific instrument is. Continue reading

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Summer FM DX: Drive-by Sporadic E

Many thanks to SWLing Post contributor, TomL, who shares the following guest post:

Summer DX – Sporadic E, FM band

“Sporadic E” DXing is a specialty of some DXers.  I have never dabbled in it being content with mediumwave or shortwave listening.  However, it was truly fun to spontaneously hear this happen while driving on the Interstate highway, Wednesday August 4 around 6pm Central Time.

To quote from an ARRL propagation article:

“As frequency increases still further, signals will eventually pass through the F1 layer to the F2 layer. Because this is the highest reflecting layer, the distance spanned by signals reflecting from it is the greatest. The maximum skip distance for the E layer is about 2000 km. For the F2 layer that increases to about 4000 km—a significant gain.”

I was listening to the local classical music station WNIU in DeKalb, IL which is a good 50 kW transmitter about 10 miles behind me near the Interstate highway.  A different station was breaking through. Eventually, I heard a familiar Christian song “You Make Me Brave” swamp the classical music. I noticed it was a remake of a song made about 10+ years earlier. The two signals fought it out and then I heard the station ID “Spirit FM” and a short humorous segment called “Attitude Adjustment”, then more music.  Finally the local classical music station won out and I thought I would look up the station ID of that contentious station later.

When I googled “90.5 Spirit FM”, it came up with a station in Tampa Bay, FL called WBVM. Cool!  Just to be sure, I went to the station web site and looked up their playlist and this confirms what I heard:

Curious about the transmitter, Radio Locator said it was a 100kW station and gave the Long/Lat coordinates.  I then went to Google Earth and mapped an approximate distance of 977 miles (1572km), give or take 10 miles:

I did not have time to get on the shortwave radio to see if the 10 meter band was busy since I had things to do.  But it is a very nice surprise to hear in my old car radio an FM station almost 1000 miles away. For one thing, Analog radio is still fun.  Secondly, things are busy this summer if you are at the right frequency and time!

Happy Listening,


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Guest Post: Recording Music on Shortwave Part 2 – Weak signal recovery

An example of an AirSpy SDR# software screen.

Many thanks to SWLing Post contributor, TomL, who shares the following guest post:

Recording Music on Shortwave Part 2 – Weak signal recovery

by TomL

The QRM noise cloud surrounding my condominium motivated my first foray into noise reduction software to find a little relief (Please refer to Part 1 posted here) using SDR recordings.  I was able to use the freeware software Audacity to reduce some of that type of noise to tolerable levels on strong broadcasts.  But what about non-condo noise, like out in the field??

NHK Japan

I took my trusty Loop On Ground antenna to the usual county park Forest Preserve which is relatively low in RF noise.  I did some usual recording on 25 meters and poked around for something being captured by SDR Console.  On 11910 kHz is NHK broadcasting daily from Koga, Japan.  It is hearable at this location but is always an S7 or weaker signal despite its 300 KW of power no doubt due to being beamed away from the Midwest USA.

I recorded it using the SDR Console 10kHz bandwidth filter and created a separate noise recording from a nearby empty frequency.  Here is the 2 minute portion of a Japanese music teacher. No noise reduction was applied:

I opened the noise and broadcast recordings in Audacity to see what I could do.  Part 1 of my previously mentioned post details how I apply the Noise file.  A big downside of using any kind of noise reduction software is that it is ridiculously easy to destroy the desirable characteristics of the original recording.  Applying too much noise reduction, especially in the presence of constant, spiky lightning noises, will create both digital artifacts as well as very dull sounding results.  So I used the Effect – Noise Reduction (NR) feature very carefully.

In this example, I used the Effect – Amplify feature on the one minute noise file.  I applied just +1dB of Amplify to the whole file.  Then I highlighted a 10 second section I thought was representative of the general background noise and chose Edit – Copy.  Then, I opened the broadcast file, Pasted the 10 seconds of noise to the END of the file and highlighted just the 10 seconds of noise. Then I chose Effect – Noise Reduction – Get Noise Profile button.  Amplifying the noise file by +1db does not sound like much but it seems to help according to my tests.  Anymore than this and the Noise Profile would not recognize the noise without destroying the music.

I used the NR feature three times in succession using the following (NoiseReduction/Sensitivity/FrequencySmoothing) settings:  Pass1 (3dB/0.79/1), Pass2 (2dB/1.28/1), Pass3 (1dB/2.05/0).  Part of what I listened for was choosing the Residue circle and Preview button for any music or dialog that was being filtered out.  If I heard something that came from the desired part of the recording in Residue, I knew that I hit the limit concerning the combination of Noise reduction and Sensitivity settings to engage.  I used those Residue & Preview buttons over and over again with different settings to make sure I wasn’t getting rid of anything wanted.  I also used the higher Noise reduction with lower Sensitivity to try to get rid of any momentary spiky type noise that is often associated with SWLing.

I messed around with a lot of test outputs of differing dB and Sensitivities and a lot seemed to depend on the strength of the broadcast signal compared to the noise.  If the broadcast was weak, I could push the dB and Sensitivities a little harder.  I also noted that with strong signal broadcasts, I could NOT use more than 1 dB of Noise reduction beyond a Sensitivity of about 0.85 without causing damage to the musical fidelity.  This was a pretty low level of nuanced manipulation.  Because of these minor level Audacity software settings, it dawned on me that it is very helpful to already be using a low-noise antenna design.

If the Sensitivity numbers look familiar, that is because I tried basing the series of Sensitivity on Fibonacci numbers 0.618 and 0.786.  Don’t ask me why these type of numbers, they just ended up sounding better to me.  I also needed a structured approach compared to just using random numbers!  Probably any other similarly spaced Sensitivity numbers would work just fine, too.

Now if you really want to go crazy with this, add Pseudo Stereo to your favorite version of this file (also detailed in Part 1) and playback the file using VLC Media Player.  That software has a couple of interesting features such as an Equalizer and a Stereo Widener.  You may or may not like using these features but sometimes it helps with intelligibility of the voice and/or music [VLC will also let you right-click a folder of music and choose to play all it finds there without having to import each MP3 file into a special “Library” of music tracks where they bombard you with advertisements].

You can also turn on Windows Sonic for Headphones if you are using the Windows operating system.  However, this can sometimes be too much audio manipulation for my tastes!

Here is the resulting NHK noise-reduced file with 9ms of delay with High & Low Filters:

Radio Thailand

Five days later I was out in the field again.  This time I found Radio Thailand on 11920 kHz finishing up a Thai broadcast.  It was a weaker S5 signal than the NHK example, so it would be a good test.

When I got home, I recorded the broadcast file at a Bandwidth filter of 8 kHz and using Slow AGC and the extra Noise file at 12kHz using Fast AGC.  In a previous test I had noticed a very slight improvement in sound quality in the way noise seems to get out of the way quicker compared to Slow AGC (which is usually how I listen to shortwave broadcasters).  I now try to remember to record the Noise file with Fast AGC.

Here is the original without any noise reduction:

This time the Noise file using Amplify +1dB did not help and I used it as-is for the 10 second Noise Profile.  I then tried multiple passes of NR at higher and higher Sensitivities and ended up with these settings the best: Pass1 (1dB/0.79/0), Pass2 (1dB/1.27/0), Pass3 (1dB/2.05/0), Pass4 (1dB/3.33/0).

As a comparison, I tried recording only with SDR Console’s noise reduction NR1 set to 3dB and got this.  I hear more noise and less of the music coming through:

Now for more crazy Pseudo Stereo to finish up the Audacity 4Pass version (nice Interval Signal of Buddhist bells ringing and station ID at the very end):


I do not understand why applying 3 or 4 separate 1dB Sensitivities of noise reduction is superior to just one Pass at 3dB Sensitivity (in Audacity) or the one 3dB noise reduction (in SDR Console).  My guess is that doing 1 dB at different Sensitivities shaves off some spiky noise a little at a time, somehow allowing for more of the musical notes to poke through the noise cloud.  Who knows but I can hear a difference in subtle musical notes and sharpness of voice and instruments.  Probably the Fast AGC helps too.

Music is a Universal Language that we can share even when we don’t understand a word they are saying. And there is more music on the air than I thought.  Some of these recordings sound surprisingly pleasing after noise reduction. The fake stereo is pumped through a CCrane FM Transmitter to a few radios in the home, or I can use the Beyerdynamic DT990 Pro headphones.

Enjoying the Music!


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Reminder: Comb Stereo Broadcast via Radio Gum Tree–June 18, 2021

A quick reminder that the rebroadcast of Radio Gum Tree Episode 2 will take place tomorrow: June 18, 2021 at 9:45 EDT (or June 19, 2021 at 01:45 UTC) on on 5850 kHz. You can find the program notes for these Test broadcasts at this web site address: www.radiogumtree.com/?p=54

Many thanks for putting together this Comb Stereo series, TomL!

For more information, check out TomL’s initial announcement.

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More Comb Stereo Broadcasts via Radio Gum Tree June 18 & 25, 2021

Many thanks to SWLing Post contributor, TomL, who notes:

Episode 2 of Radio Gum Tree will be rebroadcast this coming Friday night June 18, 2021 at 9:45 EDT on on 5850 kHz in case anyone missed it. Episode 3 should be on June 25.

You can find the program notes for these Test broadcasts at this web site address. I will not be archiving the broadcast on the internet due to music copyright concerns.


Many thanks for putting together this Comb Stereo series, TomL!

For more information, check out TomL’s initial announcement.

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Four weeks of Comb Stereo tests via WRMI!

Many thanks to SWLing Post contributor, TomL, who has put together a four week series of Comb Stereo tests that will be aired on WRMI. Here’s the full announcement:

Starting this Saturday June 5 at 01:45-02:00 UTC (Friday 9:45pm EDT), I will be conducting a four-week series of tests using Comb Stereo. The broadcast will be aired on WRMI on 5850 kHz and will only be 15 minutes long. It will feature two minutes of “CNN” news by a computerized voice (sorry, I am doing this on-the-cheap!). Then, what follows is about 12.5 minutes of music encoded with Comb Stereo.

For you, the listener, to hear the Comb Stereo, you will need to record the broadcast to your digital recorder or SDR software and then play it back through your Windows PC using the instructions at the bottom of this announcement. I welcome feedback regarding such things as, 1 – I heard the broadcast and recorded it, 2 – I tried to setup my Windows PC but could not get the CSDecoder and Virtual Audio Cable to work, 3 – I got those things to work and opinions about what the stereo sounded like.

To repeat, you will not hear stereo unless you send your recorded audio file through the CSDecoder.

Do not expect FM Broadcast quality since Comb Stereo is a rudimentary form of creating two-channel sound. For instance, you may hear the stereo separation waiver a bit, or the sound stage image may wander, or a slight hollow sound at times. Sure, OK, but this is also a chance to hear stereo from a shortwave broadcast. So let me know your thoughts by sending feedback to [email protected] and I will tally up the results and post the findings here on the SWLing Post Blog.

Many thanks to Daz and Roseanna at Radio Northern Europe International for making the Comb Stereo available and to WRMI for the use of their transmitter.


P.S., please don’t mind the look of the web site at www.radiogumtree.com, it is still under repair and the web hosting company has to fix something or I end up replacing them!

RadioGumTree.com is a personal, eclectic look at Radio, Music, the Universe, and Beyond. For feedback or questions, please write to [email protected]. For program notes, please visit the Blog section of radiogumtree.com for more details.

The broadcast itself will not be archived on my web site due to copyright concerns.

For Radio episodes that are encoded in Comb Stereo, go to this web site for instructions on how to install the Comb Stereo decoder: https://rnei.org/stereo/

For an example of a guided user install of CSdecoder and the needed Virtual Audio Cable on your Windows PC, go to this blog post: https://swling.com/blog/2021/05/guest-post-listening-to-comb-stereo-on-shortwave/

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Guest Post: Listening to Comb Stereo on Shortwave

Many thanks to SWLing Post contributor, TomL, who shares the following guest post:

Comb Stereo on Shortwave

by TomL

Comb Stereo is an old technique being implemented over shortwave by the main sound engineer (Daz) at Radio Northern Europe International (RNEI).  It ONLY works on Comb Stereo broadcasts which currently are RNEI, This Is A Music Show (WRMI), and one of the KBC broadcasts.  It works in real-time or for SDR recorded files, too.  It does NOT need a special HD/DAB+ radio.

A number of pluses for Comb Stereo on shortwave compared to digital:

“The bandwidth is the same as mono – So the SNR should be about the same as mono.

Selective fading doesn’t affect the comb bands much, so the balance is largely unaffected by selective fading notches.

The Comb Stereo artifacts are much like typical music effects of echo, chorus, fast reverb or room reflections.”

You can read about it here on Daz’ web site: homepages.ihug.com.au/~daz2002/tech/CombStereo/

You can also read Roseanna’s comment on the SLWing.com blog post: https://swling.com/blog/2020/04/rnei-now-broadcasting-in-comb-stereo/

An enhanced version is broadcast on WRMI for the RNEI time slot on Thursday morning (01:00 UTC) on 5850 kHz.  It sounds very good and is not a pseudo-stereo like in my previous article, Music on Shortwave.  For one thing, pseudo stereo is not real two-channel encoding and shifts vocals to one side, depending on which channels are chosen for high and low filters, which might get annoying after awhile.  What seems amazing to me is that I have been able apply some minor noise reduction in Audacity and the Comb Stereo stays perfectly intact.  It also still works after converting the WAV file to MP3 and sounds much like a regular FM broadcast.  Furthermore, it does not require a special patented transmitter or receiver chip.  It is compatible with regular mono transmitters.

If you want to try it, go to the RNEI web site; download and install the two files listed (VB Audio Cable and CombStereo Pedalboard x64):


It is slightly tricky to setup and use or you will not hear anything (most Windows systems default to 48000 Hz these days).  Right-click on the lower-right taskbar Sounds settings.  Make sure to setup Properties – Advanced in both the VB-Audio Virtual Cable (Playback and Recording) and your output speakers (Playback) to 24-bit 44100 Hz processing.

Now run the app Pedalboard BAT file which corresponds to the broadcast you recorded (in this example “Start Comb Stereo for WRMI.bat”).  Set the Options – Audio Settings:

Since the VB-Audio Virtual Cable takes over your volume output, adjust the volume of your Speakers in Windows’ Sounds – Levels (or you can adjust the volume in the sound player you are using, too):

Play the mono WAV or MP3 file and you should be hearing stereo!

When you are done, close Pedalboard2 and then disable the VB-Audio Virtual Cable for Playback and Recording to get your Sounds back to normal:

I cannot demonstrate what it sounds like unless you have the VB-Audio Virtual Cable and the Comb Stereo app setup and working properly.  Here are snippets from recent RNEI broadcasts captured by my noisy porch antenna:


Here are links to the artists’ YouTube videos for comparison:

Kari Rueslåtten – https://www.youtube.com/watch?v=SFN4O3YrUG4

Ani Glass – https://www.youtube.com/watch?v=T63QS9enT-A

What is nice is that I can create a space-saving MP3 mono file and this setup will decode the stereo when run from the computer (sounds really nice on a stereo system with a subwoofer).  Unlike digital, this analog-friendly stereo seems mostly immune to fading, has a minimum of digital artifacts, and will not go silent and “drop out” like digital does for long, annoying periods of time.  It is not perfect stereo but audio players with features like Stereo Widener or Windows Sonic for Headphones can overcome some limitations.  Perhaps content providers should consider Comb Stereo for all their shortwave radio shows since it is perfectly compatible with mono AM transmissions!

Enjoying the Music,


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