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Author Topic: Crummy Computer Recording  (Read 1978 times)
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ki4nr
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« on: June 06, 2023, 07:36:21 PM »

I'm trying to figure out whats up with my computer. The last week I been bread boarding a AM modulator for my Icom 756pro. After playing around I got one that works great, way beyond my expectations. Been testing by listening in my Sony MDR-7506 headphones, I got this great idea of making a recording on my computer. No revelation as everyone has done this, I just have never bother with it.

So my monitor bench radio is also another Icom, the 746Pro. I got a good deal on it and it has a super receiver, ultra flat audio on AM 80hz to 5khz clean DSP detection and 3.65k on SSB.  I wire up a cable from line out on the back of 746pro to the line in on the computer, turns out the level is to hot for the computers on board audio. So I make a simple resistor attenuator to drop it down. I go get my Yamaha stereo receiver from the living room make another cable from computers line out to receivers AUX . Hook the receiver up to my Polk bookshelf speakers I normally use at my station.

The 756pro is in the dummy load running 10 watts carrier the 746pro is connected to my in line adjustable RF sampler I built. The 746pro is getting a 20 over 9 signal, same setup I been using for a while.

I fire up audacity program to make my first recording. I set all audio levels and everything is perfect. No hiss, no ground loops. I make my recording and take a listen, expecting the super audio I just heard in the headphone connected directly to the 746pro headphone jack.  What did I hear out of the polk's , the worst washed out crummy audio ever. Sound like a washed out low resolution crap. It's not distorted at all just sounds flat & dull, lifeless. I checked all settings both in Audacity and sound card everything is at highest setting for best audio.

I played with this for a day and I checked it all,  line levels, computer setting, nothing is overloaded. It should make a perfect copy of a narrow 100hz to 5khz signal, but it does not for some reason. If I plug the headphone in the Icom 746 it sound unbelievable good, live me talking. I have the headphone jack running into another input on the Yamaha receiver and I can switch to it.  If I set the downward expander on the 528E up to cut the feedback out for live transmission, the sound I hear out of the polks is unreal sounds like a wide band PA system. But make a recording on the computer and played it's line out into the same Yamaha receiver and polk speakers and its crap.

The computer I have is an Dell desktop about 8 years old. But I figured any computer should be able to make a close to perfect recording on our narrow audio bandwidth. Heck any cheap 1980 cassette deck can do that with ease. Computer sounds fine to me on Youtube and playing music files. But narrow band audio resolution is junk.  Anyone have any Ideas why decent computer is making a crummy recording ??
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W7TFO
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« Reply #1 on: June 07, 2023, 12:01:07 AM »

Maybe RF is getting into it on the input line.

73DG
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ki4nr
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« Reply #2 on: June 07, 2023, 08:03:49 AM »

Yea, I thought that too, I dropped the output on the 756pro down to milliwatts, still sounds the same. I even put inline a hi end car stereo buffer/preamp that I have in both the input and output of the computer , figuring there might be an impedance match issues, that did nothing still same sound. So I'm back to listen on my sony 7506 headphones plugged into the 746pro , that sound's super good !! Sure wish I still had my Nakamichi cassette deck. That would make a flawless analog recording.
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KA3EKH
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« Reply #3 on: June 07, 2023, 08:47:43 AM »

Check your settings! 44.1 or 48K Wave format, MP3 sucks. If you just use the Sound recording tool in accessories it will do a great job, Audacity, Garage Band and ProTools are overkill for something that simple.
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N1BCG
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« Reply #4 on: June 08, 2023, 09:23:00 AM »

Divide And Conquer!

If you know the audio coming from the monitor receiver is good then try using another source for audio such as the line out of an FM receiver fed into the soundcard. This will verify the condition of the soundcard input and recording settings.

BTW, if you have a separate line in and mic in, be sure that you're using the line input (blue) and not the mic input (red). Also be sure in your audio device settings that the line input is the only one enabled.

The MP3 format is fine. Record labels send new releases out at 320kb, 44.1kHz. If it's good enough for them it's plenty good enough for your test.

It may also be good to reduce the RF level to the receiver. Anything over an S-9 will cause the AVC to work harder. Ideally, the AVC should be disabled and the input signal reduced well below the detector drive limits. That will give you the most accurate signal assessment.
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KA3EKH
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« Reply #5 on: June 08, 2023, 02:04:51 PM »

Not saying you got to run at 192 kHz/24 bit but for myself will always stand by 44.1k/16 bit being the minimum for anything that is important. OK, so maybe MP3 are good enough for you but the problem I have is that I have had too many people bring in crappy 8-bit MP3 files they downloaded from the internet and wonder why they sound like that and isn’t there some way we can clean them up? Once you compress a file the information will never be any better then what you have at that point, if you want to hear what something sounds like its PCM or Wave, not some format that’s going to squash it down for fast download. Then again that’s just me, your experience may be different.
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K8DI
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« Reply #6 on: June 09, 2023, 08:09:48 PM »

A quick look at the manual shows multiple ways to get audio out the back of an IC746pro, none of which are labeled exactly “line out”.. how exactly are you getting the audio? And does your cable setup account for the mono radio connected to the stereo computer?  My guess is you have a significant impedance mismatch along with a level issue …or a broke computer..or a completely wrong Audacity setup. Your D104 recording/curve is wrong, too. They do NOT respond like that. So…something is wrong.

Ed
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Ed, K8DI, warming the air with RF, and working on lighting the shack with thoriated tungsten and mercury vapor...
ki4nr
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« Reply #7 on: June 10, 2023, 05:56:55 PM »

Yep, the computer has a problem. After looking at the curve/sound I was getting and the crazy D-104 response it had to be the computer. Then it dawned on me, last summer I was watching a movie at 2 in the morning and I hear thunder in the distance. Well it was closer than I thought, next thing I know there's a flash / bang and all the house goes dark.

Lighting hit the line down the road so hard it blew the fuse on my pole pig which I saw in the morning light. Fearing the absolute worst and ready to call my insurance company. The Lineman replaced the fuse and I went in the house to assess the damage. Lucky me nothing was hurt, everything came back to life.  Before the strike, all my radio gear completely disconnected.

Well everything came to life except my modem. It was history but my computer was fine, so I thought. I got a new modem but the computer would not connect, did everything I know nothing. So I concluded the onboard interface was zorch. Look on the mother board for damage but nothing. Well the USB was working fine so I took a chance and got one of those USB to ethernet adapter, works like a charm back up and running.

So to my audio problem, went over to my friends and borrowed an old XP machine. Oh yea !!  got good audio now !! My new modulator on 756pro sounds like a million. It's amazing that Icom's DSP with 9 zillion transistors and complication can't make nice AM. My simple analog three transistors modulator in the 455 IF just blows it way in every category. Well at least the DSP unit makes a nice carrier for my new modulator !!
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