TX Audio Distortion - Video Uploaded - Normal Quality?

[PapiChulo-W7]

I am now on my 2nd sample of an already ready-built truSDX from approved seller on Amazon.com, thinking perhaps I had one with an assembly problem. But...the TX audio distortions are the exact same in the 2nd unit!

I've read the reports of other people having similar issues, and my on-the-air audio reports are very poor. Problem is...WHAT QUALITY of SSB audio should be considered "normal" for this radio? I could not find enough audio samples online to make a judgement, so I made a test myself.

Before recommendations, I have read the "fixes" and tried them all except reinstalling the bootloader. (Other people have reported the bootloader "fix" did nothing at all.) I have done a hard reset, upgraded the firmware to the latest beta version, tried an external microphone, made sure there were no devices emitting RFI in the area of my test setup, applied ferrite chokes - etc etc etc. None of these "fixes" has cleaned up the TX audio, not one single bit.

I have noticed that the TX Drive and Noise Gate settings in the menu do have some effect on audio quality. I have experimented with them, and found the best setting was #2 TX Drive and #4 Noise Gate. Bandwidth settings also have a minor effect on audio quality too. I made sure that I was not overmodulating the rig by use of the modulation indicator in the new beta firmware.

So...the questions remain - 1) Is this raspy, scratchy distorted audio "normal" for the rig? 2) Are perhaps both of the rigs I got from this vendor equally faulty in performance? 3) Is there anything else I can try to improve audio quality to where people don't mention it to me during a QSO?

Listen for yourself...here is my video. PLEASE tell me if this is normal or not? Thank you.

https://youtu.be/zYh4oq-R_c8

[PapiChulo-W7]

I forgot to mention that I also tried an external microphone on the rig, in case the tiny mic element was damaged through too much heat during soldering. NO IMPROVEMENT in TX audio quality.

[Ohwenzelph]

I thought the 4khz setting at one foot away sounded ok. Never going to sound hi if, it is qrp audio made with an 8 bit processor. From the beginning the generated audio has never been terrific but you are able to be understood and to communicate, and trying to make it better has been on the wish list from the beginning. I really don’t know if the transmit audio on yours is normal or not. It would be nice to know. There have been rigs that have been identified as worse than average. Manuel had one and was going to trouble shoot it but for that particular one reloading the bootloader was enough.
Thanks for posting it on you tube.

[PapiChulo-W7]

Thank you for watching and commenting. I believe that 8 bit audio can be of rather shocking high-fidelity. I’ve downsampled 16 bit CD music to 8 bits and it was still very good. I think that the sample rate has much to do with its fidelity.

I still don’t know if my rig is “typical” or has some functional issues, I’m trying to find that out with this post.

If the distortion is just inherent in the design, is it the digital audio chain at fault, or is it distortion in the Class E PA stage? I wonder if there are any plans to improve audio through software or hardware modifications?

I may try flashing the boot loader again, but presently don’t have the proper hardware tools to do so.

73,

[Nehem11e]

Did you come across this post:

https://forum.dl2man.de/viewtopic.php?p=7281#p7281

It seems there is a distinct (tr)uSDX sound. Also that post like others indicates that if you aren't getting splatter then you dont need to reflash the boot loader.

I get similar audio quality reports I "seem bassy", "lack treble", or just "audio distortion"

I find setting the Tx drive to 2 makes it sound a little better. I also seem to get more of those comments when I am on the mid to lower frequency bands like 40, 60, and 80m.

[PapiChulo-W7]

Nehem11e:

Thank you very much for that video link! Having only 20 dB TX dynamic range, with artifacts present below that range, explains everything. I was listening to myself on a Web SDR today, and my signal was weak, perhaps only 12 - 15 dB peak above the noise floor. My audio sounded great! Reason: All of the distortion artifacts were buried down in the noise!

I did some 40m on-air testing today with people I trust. My signals were about S5-S6 peak, so about 20-25 dB above their S2 noise levels. I had the SDX set to #4 on both Noise Gate and TX Drive. We tried all four bandwidth settings, and three different speaking distances away from the internal mic: 3", 6" and 12". The easy winner for lowest distortion was the 4 kHz BW, speaking 6" from the mic. Interesting enough, the listeners could not see or hear a great difference in audio bandwidth as I stepped to narrower filtering! More on this in a bit. I'm going to do some more testing with them and try lowering the TX Drive level as you suggested. BTW, the Noise Gate setting has a pretty strong effect on TX audio quality as well. I'm not sure why.

One issue with the rig (internal mic?) is the serious lack of high frequency energy. I've attached a screen shot of my audio test from today. The spectrum is my signal, and the waterfall below is me from 0 - 12 seconds, and another Ham's signal from 15-20 sec (note his audio has a lot more high frequency energy compared to mine). Note my big peak in energy close to the carrier (low frequencies) and a sharp drop off for the high frequencies. This is the exact OPPOSITE of what we want for good intelligibility over SSB. As you mentioned, the truSDX sounds very bassy and muffled. I do not know if it is the internal microphone providing this upside down response, or if the actual SSB generating scheme has an issue. I'm going to try an external microphone to see if that has any effect, or possibly feed an audio signal generator into the rig and measure it's transmitted frequency response.

Since we have just 20 dB of TX DR to play with, I'm thinking that perhaps an external mic running a small amount of gain compression with high-freq-boost EQ might do wonders to improve the TX audio quality and communications efficiency. This is all left to experimentation, which for me is a big part of the fun.

I'll be posting my results as I go along.

73, W1LJ

[Nehem11e]

Well I can certainly agree that experimentation is a very big part of the fun.

I would be happy to help if I could, but you certainly sound like you know what your doing. I definitely like the idea of an external mic running a small amount of gain compression with high-freq-boost EQ. I might also see if I can figure out how to do that.

At the 14:50 time mark in this video:
https://www.youtube.com/watch?v=gW5r5JQRbus&t=1033s

DL2MAN, mentions that there is more to noise gate than just the the VOX trigger threshold. Its microphone sensitivity and then some but he self admits that he is more CW and doesn't use that function. I will search this forum to see what I can find.

Keep us posted on your testing! I will let you know what I find.

Abe
KC3WOA

[Nehem11e]

Here is a post detailing some info on the noise gate:
https://forum.dl2man.de/viewtopic.php?p ... gate#p5845

[Nehem11e]

Here is a link from the kit builder suggesting a small drill hole so more treble sound pressure can get in.
https://forum.dl2man.de/viewtopic.php?p=5084#p5084

An external mic test should bypass this.

[Nehem11e]

This post reminds me how impressive what we are getting with the hardware we have. It also suggests "Noise Gate set at 8 and TX Drive set at 4 the audio" works well on 60m

https://forum.dl2man.de/viewtopic.php?t=645

[PapiChulo-W7]

Nehem11e, thanks for all those links. Very helpful!

My next experiment will be to drill a larger hole in the center of the internal MIC location and check the freq response. From there I'll be trying the external Pacific Antennas electet microphone, but will need to find a way to power the capsule. Perhaps I'll incorporate a very small plastic box to house the battery AND also place a tiny compressor/EQ circuit in there. Being a SOTA op, the whole idea for me is to keep things as small and light as possible - the only reason I bought the (tr)uSDX. Otherwise, I'd use my FT-817 which has a far better receiver and excellent TX audio, being an analog rig. But...it is relatively BIG and HEAVY, not to mention having considerable battery drain!

[Nehem11e]

Before drilling the hole you could just take off the front faceplate to see what it sounds like without anything the way

[flyingalan]

If you haven't seen this, the contributers last year did some similar tests. The conclusion was that a filter design with gain giving an hf lift seemed to help intelligibility. When I get time I intend to build the 2 transistor filter design circuit he published. The posted audio clips seemed quite convincing for improved readability. It's never going to be hifi but it seems some audio response shaping can help.

http://forum.dl2man.de/viewtopic.php?t=870
Regards
G8ALQ

[PapiChulo-W7]

If you haven't seen this, the contributers last year did some similar tests.

http://forum.dl2man.de/viewtopic.php?t=870
Regards
G8ALQ

Thank you, Alan!

[Nehem11e]

Good find/recall Alan! I might try and look and see if I can find somewhere that can build the PCB

Something that popped out at me in that thread was using tx drive as a pseudo compression. I guess it is sort of compressing because it is bringing the lower levels up.

What about using something like this for testing
https://www.sweetwater.com/store/detail ... izer-pedal

I have tried using my laptop and some software eq processing, but this is new to me.

[Nehem11e]

For anyone who might be looking into that equalizer pedal hold off because that is expecting instrument level signal not mic level signal.

[Nehem11e]

With regards to the software solution. I did get garageband installed on my Mac. Which wasn’t simple because the version of garage band through the App Store isn’t compatible with my old Mac. But I found an old installer.

It can do what I think you were originally thinking or the filtering that the circuit Alan found can do. Time for testing!

[Nehem11e]

Dennis,

I haven’t gotten much testing done, but here is another video and around time stamp 31:00 Guido is talking about SSB audio quality
https://www.youtube.com/live/3D36p-_eQD ... rE1UVh1Lqg

He is saying the same thing about 46db of dynamic range. So I am not sure if more info is provided but I wanted to add the link to this thread

Abe

[pe1nnz]

The speech in the first post sounds in the first instance indeed clipped and over-modulated, later when the microphone is hold further away it sounds more normal as what it is supposed to sound.

Wondering what firmware you used and which pa bias settings. The best settings generally are noisegate=2, drive=4, pa_bias_min=0 max=128 for 3xbs170 or 128..180 for fdt86256.

Later firmware version 2.00u have a fix for internal overload and represent an overload indicator on screen (999) when there is too much input.

Regarding the bassy sound, the natural voice do not have an equalized output, so this might be the case as the trusdx does not compensate for that. Thanks for the input.

[gatorjj]

If you haven't seen this, the contributers last year did some similar tests. The conclusion was that a filter design with gain giving an hf lift seemed to help intelligibility. When I get time I intend to build the 2 transistor filter design circuit he published. The posted audio clips seemed quite convincing for improved readability. It's never going to be hifi but it seems some audio response shaping can help.

http://forum.dl2man.de/viewtopic.php?t=870
Regards
G8ALQ

I haven't been around the forum in a bit and was catching up when I saw you referring to the activity we did last year on transmit audio. I'm the one who hacked together that design, if you build it I'd love to know how it works out for you!

I built 2 of them (one for each of my (tr)usdx radios) and I guess it's going on close to a year with good results still. Since Guido implemented the audio level, I mostly see 999 with this when talking but it still sounds the same and I don't think I've had a negative audio report (nor a positive one either for that matter ). I use these (tr)usdx mainly for POTA and though I mostly do CW, I usually do some SSB too and especially when signals are very weak it makes a big difference in intelligibility.

It may also have some to do with the mic itself, I used an element from a cheap broken PC lapel mic and worked the circuit specifically with that mic. I was really out of my element making this, a lot of trial and error and going with what my ears told me...so you may want or need to tweak some things.

Good luck!
J.J. KF4VE