Very simplistic front with indicator lights built into plastic snap shut box:
Inside with lid opened on plastic outer box and lid of inside metal shielded tin removed:
Cool little trick I learned for making cheap labels. Print them using a regular printer, then use wide clear boxing tape and tape over them to fake laminate them. Do the same to the back side of the labels also this way when you cut them out and glue them the glue itself won't make the ink blur or fudge. Superglue that has the tiny brush included works best but be careful since it takes care or else you'll have a label stuck to your hand or where you don't want on your project. Still beats the hell out of old fashioned label makers or a magic marker!
The plastic box is ugly, but I don't care. This is audio, no one hears the way the project looks! ;D In the future I would like to etch a proper circuit board, and/or at least transfer the whole design to a proper rack mount box. That may be wishful thinking though because I am broke.
As you can see there is still a tiny bit of space in that box and if I wanted to I could use a simple all in one IC chip stereo MPX generator and add that to a tiny perfboard and mount it inside and add a final MPX output BNC jack connector. Doing that would make the project a complete all in one FM processor, but for now I just let my transmitter do the stereo coding (with pre-emphasis disabled) and plug this box into it to do all the compression, pre-emphasis, filtering, limiting, and final clipping.
PS: Oh and as you can see lately I am using my online name "Kage" as my fake brand name for things I make. I hope the name isn't taken for actual electronics brand because I like the name and it is a play on a combination of letters from my real life full name.
EDIT: August 15, 2020, re-uploaded images since tinypic no longer online
Kick ass Kage!! That looks very professional! At first look, and if it was not mentioned, I bet many would not even think that is a home brew design and in prototype stage!
F*&ing Excellent!!!
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Great right up Kage, my question to you is where does this go in the chain of equipment, I'm guessing the end of the line before the transmitter. I do not have the skills to build something like that yet so I had to order mine. In the "tutorial:starting out" thread you can see my setup with the new mixer so would my compressors/limiters go from my mixer output to my transmitter input??? Question 2: you mention the pre-emphasis is disabled on your transmitter when I get my new equipment (transmitter and limiter/compressor) they both have pre-emphasis settings,should I just use one? and if so which one.
Great right up Kage, my question to you is where does this go in the chain of equipment, I'm guessing the end of the line before the transmitter. I do not have the skills to build something like that yet so I had to order mine. In the "tutorial:starting out" thread you can see my setup with the new mixer so would my compressors/limiters go from my mixer output to my transmitter input???
The audio processor connects directly to the radio transmitters audio input. There should never be anything between the transmitter and the processor in a proper setup.
When only using a limiter/compressor I would place it before the transmitters input as a last resort of peak limiting the audio so not to over-modulate.
Question 2: you mention the pre-emphasis is disabled on your transmitter when I get my new equipment (transmitter and limiter/compressor) they both have pre-emphasis settings,should I just use one? and if so which one.
If your limiter has built in 75uS pre-emphasis then use that instead of the transmitters. You only need to use pre-emphasis once or else your audio would sound exceptionally bright and distort like crazy.
The reason you want to use pre-emphasis before the final limiter (or in your case built into the limiter) is so that the emphasized high frequency audio will be hard limited and thus the audio output will not be allowed to over-modulate the transmitter regardless if it be bass frequencies or treble frequencies. If using the transmitters pre-emphasis without proper audio processing it's much more likely that high volume high frequency audio will distort and over-modulate possibly knocking out your stereo pilot and causing adjacent channel interference.
The problem comes in when using only one audio limiter since the boosted high frequency content can cause the limiter to kick in causing audio ducking of the lower bass frequencies. This is why audio processors use two limiters, one for the baseband audio and a final limiter for the pre-emphasized high frequencies.
Not to sound discouraging though. Use what you have and see what sounds best for you.
Forgot to mention that if you can't afford an audio broadcast processor (which who can at the price they cost!) or rig something together like I did you can always use something like the Sonos processor software to emulate what hardware does. You just need a good sound card that can do at least 192kHz audio and a spare computer. Laptops are great for this use since they take little power and space to run.
Here's a demonstration video someone made with links to the software if interested..
Personally I only toyed with the software and couldn't get it to work properly on one of my computers but others have had luck with it.
Holy shit ever wonder how bad your FM audio processor sounds or your setup without any kind of processing?
This is THE test song to try...
Heart - Alone
This song almost passed my broadcast processor I made, but it really started dying on the sibilance of her voice smearing the audio and really pressing the passband compressor making punched holes in audio at the worst passages of the song.
Still the effects were not too noticeable when running the input gain on par with the line level input, in other words not pushing the first limiter to limit!
Even past the first limiter stages level it still sounded good but I could really hear parts where the crystalline vocals punched holes in the rest of the audio but remind you I hear things that 90% of my listeners don't or care about so this may be a mute point.
The funny thing about this specific song I mention is that it is well known as a test song for FM broadcasters. Many people who play around with broadcast processing use this song as a do all die all song. Either it sounds good through the processor or it sounds awful.
Now for those of you not using an audio processor or any kind of aid to limit audio you should easily be able to play this song and all hell should break loose. Try it!
It amazed me when I first played this old song figuring how bad can it be? Well I learned a quick lesson in the difference between dynamic CD quality audio with emphasis on FEMALE vocals compared to regular anything else. Holy shit talk about a difference between distortion and pumping compared to leveling and regulated compositions.
I am very curious to have you all test this song on your setup and get back to me. Don't feel bad if it kills your audio. Even the best most expensive audio processors fail somewhat on this Heart song.
Please get back to me after you're done crying.
The final conclusion is that analog will never rival digital filtering or compression in theory, yet here I am listening to my own box through a FM transmitter into a dummy load and it sounds better using my box than using the demo breakaway digital software broadcast processing software.
The software version of this can handle cutoff points better than my box and totally kill everything at some specified point, but digital itself causes nasty harmonics from aliasing, and in truthful experiments using demo software like breakaway compared to my box my setup may not give the most loudness but it sure doesn't dramatically change up the source audio.
Post by jessewillem on Oct 21, 2012 12:40:23 GMT -6
I've been experimenting with home built audio processing too. But I'm doing it the digital way, just using an ordinary PC with sound card.
The processor I'm making features a 3 band AGC with 6 band Compressor/Limiter after the AGC. A really fast 3 band limiter takes care of deleting peaks out the audio. Its never going to sound as good as units from Orban, Omnia, BW Broadcast, but building one is a great exercise in understanding in how things work.
Also Sonos is already old, I really recommend to look at Sonos 4 from John Burnill.
It will only be as good as what is going into it. If the audio source is coming from compressed mp3 files, that is going to play a huge role in what that processor may pull out in the way of digital compression artifacts, which affects high frequency response mostly.
You may have been hearing mp3 file compression artifacts that your processor easily "pulls" out of the audio, thus hear it.
I would test with nothing but uncompressed audio files, from vinyl or high resolution digital sources like CD's etc.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
It will only be as good as what is going into it. If the audio source is coming from compressed mp3 files, that is going to play a huge role in what that processor may pull out in the way of digital compression artifacts, which affects high frequency response mostly.
You may have been hearing mp3 file compression artifacts that your processor easily "pulls" out of the audio, thus hear it.
I would test with nothing but uncompressed audio files, from vinyl or high resolution digital sources like CD's etc.
Peace!
That's why I'm always using FLAC files as source. MP3 and other lossy formats like that are only used for streaming here. And if I'm streaming to my transmitter, I use MP2 at high bitrates. MP2 doesn't have the problems MP3 has at the high bitrates, while still delivering great quality.
Here's another ironic thing to ponder. Why would anyone want to hear hi fidelity music on a pair of earphones or tiny built in laptop speakers?!!! ICK!!
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Here's another ironic thing to ponder. Why would anyone want to hear hi fidelity music on a pair of earphones or tiny built in laptop speakers?!!! ICK!!
Subscribers of Discover magazine will remember the Impatient Futurist column a few months back - The Death of High Fidelity. To sum it up, many under 30 and most all under 20 have never, ever heard music reproduced from 20Hz to 20KHz. Hence why a LOT of pop stations are playing 128-256k MP3 and try and find a lossless file outside of the Classical/Jazz genre on iTunes, HA! Rotsa ruck, shmuck!
Here's another ironic thing to ponder. Why would anyone want to hear hi fidelity music on a pair of earphones or tiny built in laptop speakers?!!! ICK!!
Subscribers of Discover magazine will remember the Impatient Futurist column a few months back - The Death of High Fidelity. To sum it up, many under 30 and most all under 20 have never, ever heard music reproduced from 20Hz to 20KHz. Hence why a LOT of pop stations are playing 128-256k MP3 and try and find a lossless file outside of the Classical/Jazz genre on iTunes, HA! Rotsa ruck, shmuck!
Cheers!
I envision a day when people of that younger age group will hear quality audio for the first time in their life and think something is wrong with it because it doesn't sound like an over compressed MP3 coming through a telephone.
A salesman at Future Shop (a preppy electronics place) was saying that kids think their CD's are defective, because they aren't "normalized" to satisfy their boom cars
Stupid me I should have socketed all of the chips. I figured out why some music was mucking up the audio on vocal S sounds and reverberated high frequency audio. My 3rd chip in the LPF stages had a bad opamp on the left part of the channel causing the audio to clip on loud passages, but leaving the other half of the chip the right side sounding fine.
So after much frustration I removed most of the opamps and put sockets in their place and then rechipped.
My God what a difference that made. I was using old JVC 4558 opamps and guess when I de-soldered one from an old trashed piece of electronics I over heated the chip causing one of its dual amps to get finicky.
Hard lesson learned, when building stuff with opamps always use sockets! Could have saved myself so much time.
Now everything sounds spectacular. I mean it did before also, but I couldn't push the HF limiter too hard w/o S sounds distorting one channel which drove me nuts. Problem solved.