Has anyone used Apple's free AU Labs plugin (under OS X) for FM audio? It contains a high and low pass filter as well as a limiter and multiband compressor. I'm just wondering if anyone has experience with settings to make it as loud as possible.
I just recently decided to "hackintosh" my PC and dual boot Mountain Lion to see if there were any cool Mac tools for this.
Currently, I set the low pass to 15k and the high pass to 30 Hz. I also turned on the multiband compressor, but it doesn't seem to make things louder. It just cuts the mid range and elevates the bass. It also seems like the distortion point of the volume level is about 88% which is weird. Under windows I usually set everything to 72%.
It doesn't sound bad but seems like it could be better with some tweeking.
Post by jessewillem on Dec 31, 2012 20:19:19 GMT -6
Most of the times, multiband compression is more used for sound coloring then making something sound loud. Loudness is most of the time done with the clipper in an audio processor.
Why not try some of the softwarematic broadcast processors (most of them run only on Windows), which in most cases can get things to sound loud and good. I recommend to check out Sonos 4, Stereotool or Breakaway. All 3 do an excellent job for FM broadcasting.
Also another problem with your approach is preemphasis. Even if your transmitter/stereo generator has it, it is still recommended to preemphasize your audio and deemphasize it before output. This protects the other preemphasis generator for overshoots, which cause a really nasty distortion.
I currently use breakaway broadcast processor in conjunction with stereo tool in windows. I use the compressor and pre-emphasis on breakaway and have Stereo Tool running as a plugin. Stereo tool handles the stereo widening and I use the FM Calibration feature in it to cut down on those nasty highs that always cause me serious issues. This was a complete nightmare to configure correctly just because of all the settings. I also have a phase rotator and bass boost plugin running in breakaway.
The reason I was looking for something else is because the resultant audio has a "manipulated" sound to it. It just isn't natural like what you hear on regular FMs. It does actually sounds pretty good, considering my cheap setup, but isn't the loudest thing on the FM dial. I was very cautious not to cause over-modulation by using a radio very sensitive to it for calibration. Whenever over-modulation occurred, you could hear the stereo narrow on the radio speakers.
In breakaway, it says not use de-emphasis for FM or AM broadcasting and I don't think my transmitter has it built in. If it weren't for stereo tool, I'd never be able to use breakaway by itself because it causes such harsh, over-powered highs. I believe this is because it's designed for digital interfaces without the "roll-off" that most cheap or on-board audio sound cards cause. My transmitter only has an analog input so I'm forced to go the analog route which opens up a can of worms.
I have also tried the standalone version of stereo tool with it's FM presets. It works pretty well, but again, THOSE DARN HIGHS! Plus, what level do you set your stereo mix and sound card output to in Windows? I've always assumed 72 (slightly less than 3/4 like the distortion point on most stereo receivers).
My reason for going the OS X route was to see if there's anything else. AU labs seems to work if I leave the compressor off, turn the limiter on, set the low pass to 15k and lower the decibel level on the low pass to prevent, again, those harsh highs.
It should be mentioned that compression or limiting only increases the average audio density, whereas clipping limits peeks therefore increasing average-to-peak ratio which is how one achieves loudness (think "wall of sound"), at the cost of slight distortion or ear fatigue depending on how much is used.
Using a multi-band compressor alone won't help much, unless it's used before the final audio processing since compression only raises average density. Multi-band compression raises that density across a range of audio frequencies while still letting loud sudden peaks get past, which is what the hard limiter and clipper cleans up while raising peak to average audio giving that louder sound. The compressors attack times and compression ratio settings will make the difference between dynamic audio and ear bleeding after running through the clipper. Release time will also play a role in loudness. Set to fast of a rate and you will hear pumping of audio, set to slow and you will loose some loudness and punch.
Without the hard limiter and clipping after the compressor you will be left with loud overshoots out of the compressor that will cause distortion if using it directly into a FM transmitter.
It's the combination of those three (compressor, limiter, clipper) that gives audio more punch and keeps things from potential overshoots in audio causing the FM transmitter to distort. To make matters even worse we need to add pre-emphasis into the audio chain, and that requires its own limiter for sibilance usually placed between the original limiter and clipper.
I currently use breakaway broadcast processor in conjunction with stereo tool in windows. I use the compressor and pre-emphasis on breakaway and have Stereo Tool running as a plugin. Stereo tool handles the stereo widening and I use the FM Calibration feature in it to cut down on those nasty highs that always cause me serious issues. This was a complete nightmare to configure correctly just because of all the settings. I also have a phase rotator and bass boost plugin running in breakaway.
The reason I was looking for something else is because the resultant audio has a "manipulated" sound to it. It just isn't natural like what you hear on regular FMs. It does actually sounds pretty good, considering my cheap setup, but isn't the loudest thing on the FM dial. I was very cautious not to cause over-modulation by using a radio very sensitive to it for calibration. Whenever over-modulation occurred, you could hear the stereo narrow on the radio speakers.
In breakaway, it says not use de-emphasis for FM or AM broadcasting and I don't think my transmitter has it built in. If it weren't for stereo tool, I'd never be able to use breakaway by itself because it causes such harsh, over-powered highs. I believe this is because it's designed for digital interfaces without the "roll-off" that most cheap or on-board audio sound cards cause. My transmitter only has an analog input so I'm forced to go the analog route which opens up a can of worms.
I have also tried the standalone version of stereo tool with it's FM presets. It works pretty well, but again, THOSE DARN HIGHS! Plus, what level do you set your stereo mix and sound card output to in Windows? I've always assumed 72 (slightly less than 3/4 like the distortion point on most stereo receivers).
My reason for going the OS X route was to see if there's anything else. AU labs seems to work if I leave the compressor off, turn the limiter on, set the low pass to 15k and lower the decibel level on the low pass to prevent, again, those harsh highs.
Dag nabbit I replied too late and didn't get a chance to read this.
First of all you don't need to use a phase rotator for FM at all. That's only useful for AM broadcast where we need it to flip the symmetry of a persons voice so that the peaks of their voice rise more positive. With FM you can't raise modulation more than 100% so it's not useful and if anything can be detrimental to your audio (especially music).
Definitely use pre-emphasis in the breakaway software and make absolutely sure your transmitter isn't using its own on-board. You should be able to tell easily by just running regular audio into your transmitter as is and if it sounds muddy as hell then you know there is no pre-emphasis built in. It's pretty obvious when you hear a transmitter on FM broadcast not using pre-emphasis. Sounds like a radio trying to come through a pillow. If it does sound normal w/o any processing then you know that it does have it and needs to be disabled in its circuitry. If that is impossible, then you need to run de-emphasis after breakaway.
Compression requires proper setting of attack, release, and ratios. Multi-band compressors obviously have 3 of those settings for each compression band. It's almost an art to get multi-band compressors to sound just right.
I suggest you get your basic audio processing sounding correct first, then worry about coloring your sound as you like.
Definitely use pre-emphasis in the breakaway software and make absolutely sure your transmitter isn't using its own on-board. You should be able to tell easily by just running regular audio into your transmitter as is and if it sounds muddy as hell then you know there is no pre-emphasis built in. It's pretty obvious when you hear a transmitter on FM broadcast not using pre-emphasis. Sounds like a radio trying to come through a pillow. If it does sound normal w/o any processing then you know that it does have it and needs to be disabled in its circuitry. If that is impossible, then you need to run de-emphasis after breakaway.
This is my problem! I can run regular audio into the transmitter and it sounds just fine. Therefore the transmitter must have pre-emphasis built in. I'm assuming that most cheap transmitters on ebay, like HLLY, CHZ, ELE, etc have it built in so the average person can simply hook it up to any device and have decent sound. I wouldn't have the technical skills to disable it on the transmitter so I'll have to look into the de-emphasis route.
I was able to solve all my issues by setting Breakaway to its defaults, setting pre-emph to 75 and turning on de-emph. Then I set my stereo mix to 100 and output soundcard to 50. I used the test tones to set the L/R Ref level which is at -2 db. I now have beautiful, loud sound coming through the radio, indistinguishable from commercial stations.
Before I was using the PEQ settings in breakaway and the graphics equalizer in stereo tool to correct the built in pre-emph on the transmitter. All I needed to do was check the de-emph option.