- March 2, 2007 at 5:54 am #6851RattanParticipant
Total posts : 27
It’s easy to get distortion and things that just plumb “don’t sound right” with transmitting. The pre-emphasis in the reciever, whatever audio filters or preemphasis your transmitter does or doesn’t have, and things like that combine to make it kind of a crapshoot so far as getting a good sound fast when you first hook things up or when you try something new like Sound Solutions or a new piece of hardware in your audio chain. You can save yourself a lot of headaches if you can get your audio chain set up so that what comes out of an actual reciever is at least close to what is coming out of where you listen at your soundcard or sound chain. if you happen to have an oscilloscope that will show audio range (I think pretty much all of them do?) *or* a spare computer (or if maybe you don’t use your computer for source or processing) and a (hardware) equalizer, it’s not really hard to do. This is another one of those “not 100% optimal, but will work fairly well and uses test gear most of us can get or borrow” things. Read through the basic setup I explained in the old thread on roughly checking modulation levels HERE. There are tips in the thread for picking up the RF directly or picking it up right at the detector to avoid any distortion or eq the reciever might add. You *don’t* want to avoid it for this though, you want to see it, so hook the input of the o-scope or the line in on a computer with winscope loaded to the line out or aux out or headphone out of the reciever. Any distortion or curve it’s adding is *exactly* what we want to see for this. Then go to Audition or whatever sound software you use for such things or grab a freeware windows signal generator or dig out your hardware audio signal generator if you have one.. Make your own test recording with at least several seconds of each frequency on the equalizer you’re going to use. Make the first one at 440 hz and about a minute long so you have time to set your basic modulation as mentioned in the “Fun with modulation” thread I gave the link to earlier. Then go through and do several seconds of each of the “bands” on the eq you’re using. Unless you play with sound enough that you’d recognize each pitch offhand, it may be a good idea to also record voice before each one saying the frequency so you don’t have to rely on counting beeps to figure out what frequency beep you’re hearing. At least if you’re on FM, then don’t bother with anything above 15 khz, since the recievers aren’t made to pick it up anyway and any sound above that is just wasting power you could be using for frequencies it *can* hear. Not sure on AM, hopefully somebody here who runs AM can tell us for sure on that. Then normalize each of the test tones so they’re all at the level you usually norm your mp3 or other audio files to. Ok, Then you hook up the equalizer in your soundchain. If you use a hardware compressor before the xmitter or the xmitter has compression like the sstran, take the compression all the way out. You can leave the limiter set where it is, assuming you already have it set at what’s good for your modulation. Then set all the sliders (or knobs) on the eq to the middle, zero. No boost or cut. And go through using the long 440 hz test tone to set your modulation as described in the other thread. Now the “fun” part. As each of the “bleeps” plays, note if it’s louder or quieter than the 440 test tone (if the wave looks bigger or distorted or smaller than the test tone) and jot down if it needs to be louder or quieter. Then go and turn them down or up on the equalizer and try again. Repeat until you have them all at least close to the same volume. Voila, your equalizer is now actually “equalizing”, meaning it’s compensating for the audio characteristics of the xmitter and a typical reciever so what you hear on your sound chain is at least very close to what comes out of a reciever. Actual music (or most other sounds we put out on the air) is more than one frequency at once. Usually it’s at least several. So take a very “loud” and “busy” piece of actual program material and play it and bring the master volume on the equalizer so you don’t see any flat-topped (distorted) waves. If you have a limiter (or compressor limiter) right before the transmitter or if the transmitter is deluxe enough to have such things, then you probably won’t need to bother with that step. If you have compression that you turned down earlier, ease it back up, you might need less of it than you used to think was necessary to get a good sound. When you’re done with all that, use “poor man’s sample and hold” by taking a snapshot of the equalizer settings with a camera or jotting down all the settings so if you fiddle with them you can get back to “zero” (where what you hear when you listen to your mix at the source is pretty much what you hear at the receiver) quick and easy. Now you can play with things like Sound Solutions, other software, or more hardware sound gear to your heart’s delight, and if you do something that sounds good on the source mix, it’ll very likely sound similarly good at the receiver. Not perfect, maybe.. But closer to the ideal of “what sounds good on the studio phones sounds good at the reciever”. As an additional benefit for those who run with a transmitter without “preemphasis”, it’ll now sound pretty much the same as if you *did* have it. Now, on the immortal question of “how many bands should an eq have”.. There are people that will tell that anything less than a 20 band (or whatever) isn’t worth bothering with. Bullcookies. Even a little 5 or 6 band can do a *lot* to level out the frequencies and if you have one collecting dust but you’d have to save up for a while to get a nice 20 or more band rackmount unit or whatever? Wipe the dust off that little puppy and make it start earning it’s keep! Pretty much all equalizers cover the range of human hearing. Ones with more “bands” just do it in smaller “slices”, allowing more precise control. That’s very useful to a soundman, but it doesn’t need a lot of bands to make the range we use for radio start sounding better. From personal experience, I’d say that most of what needs to be done in making up for the inherent frequency curves of a transmitter and reciever can be done with 5-10 bands, depending on the type of music or other program material your station carries and how much of an audiophile you are. But as long as it’s well enough made to not add an unacceptable (to you and your listener’s ears) amount of hiss/hum, even a small and humble eq is a vast improvement over no eq. If anybody wonders about this post or the “Fun with modulation” post, I have a cheap little FM xmitter I built from a kit and when I first hooked it up, it sounded awful. With some tinkering and some outboard audio gear, it sounds as good as any commercial station in the area and definitely better than some. It’s not hard to get your audio sounding good if you tackle it a step at a time and are prepared to spend some time fiddling with the controls to get it as good as you can. DanielMarch 6, 2007 at 4:01 pm #14931WILCOM LABSGuest
Total posts : 45366
Good audio will result from some hard work and the steps you have outlined above,good job Daniel! Regards,Lee
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