Before you wrap this up I have one more question about limiters/compressors, most of my MP3'S (15,000 and counting) are recorded at different levels, some louder some quieter etc. will something like this (http://www.aareff.com/en/fm-transmitter-limiter-kit.htm) equalize the sound level output so that all the songs have the same sound level???
A compressor and a limiter are different functions.
Limiter - leaves audio alone before a preset level, then hard compression above that. CBC is an example.
Compression - normalizes audio to a consistent level. Commercial stations are an example.
Compression is best as a multi-band unit, otherwise the strongest component (usually the bass) will end up compressing the mids and highs if set "too radical".
As far as I am concerned Limiting is a form of compression where the attack is very short so that little overshoot is allowed to fly by. This makes it so that audio is averaged to a "limit" overall. Of course no limiter is perfect at this, but some can get real close w/o the need of clipping overshoots.
Compression OTOH is more suited to instruments and mics. It is basically like limiting except with a longer attack setting and a shorter decay setting. This brings average volume levels up to peak levels but does give overshoot on specific peaks. When compression is used correctly it can make audio material sound louder while still maintaining the same peak average.
Leveling/limiting is simply used to bring all audio to the same volume level without care to make it sound louder. This is very useful for Automatic Gain Control AGC and the like. It is also very useful for broadcast in that it helps all forms of audio not overmodulate a transmitter.
So yes sixer to answer your question what you want is a limiter. You simply drive the limiter so that it does very light compression. If you drive it with enough audio you will hear audio pumping. The idea is to drive it so that it handles loud peaks in audio, but doesn't suck up quiet audio to loudness too badly. The simplest audio limiters have only two controls, an input level and an output level. You set the input level to your desired sound (which should be a lack of audio pumping and little suck up on quietness) and the output so that it is right at the peak of what your transmitter can handle without over-modulating.
Now if you were to add compression before your limiting then you can get a much louder sound on air at the expense of reduced dynamics in your music, much like the big boys use. Doing this though will cause your limiter to make sharp peaks above what it can normally limit which is why the final stage is an audio clipper but that is outside of the scope of your question.
Compression = make average audio sound louder compared to peak audio spikes. Limiting = make peak audio only get so loud so not to go above a specific level. Clipping = very harsh way of literally shearing off any audio in a waveform above a specific point.
Limiting is a form of compression but is more useful in broadcast so that you don't need to ride your mixer board manually with your hand to keep everything at 0dB (full volume). Using a limiter does that work for you keeping all audio at the same level above a certain point, including quiet audio depending on how much gain you increase at its input. Usually a 5db of input gain is good, this allows quiet music to ride at the same audio volume as loud music, and the listener usually doesn't hear a difference which afterall is what you want.
BTW that link you gave is for a mono limiter. You need two of them for stereo which I suppose you already know. That seems rather expensive for an audio limiter but given the company that sells it, it should be good quality. So to answer one more time, yes this is what you want
It looks like there are a few diodes on the circuit board also which may be used for final audio clipping. If that's the case then that is even better. It's hard to tell though without a schematic. Sure would love to see the schematic of that thing to see how it's built.
Thanks Kage, All my questions are now answered,and yes I know I will need two of the limiters. I believe I can request the schematics when I order the limiters so I'll let you know. As for the price I don't feel it is to bad considering I could never build one(two) myself,and they always have free shipping worldwide. What was the total cost to you for the audio processor in this thread??? Sixer
What was the total cost to you for the audio processor in this thread???
Around 4$ for the perfboard and 2$ for some solder. Seriously that's it, but only because I had all the parts already. Some from my part bin and some that were desoldered from old junked electronics that I've had for years laying around. If I were to guess what it would cost for all new parts I would say somewhere around 20 to 30$.
Audio pictorial of the processor in operation. Sorry about using notepad to notate what was going on lol but I was in a rush and downloaded a demo version of screen video/audio capturing software.
I highly recommend quality or full screen to see the text information I put in there.
The music isn't exactly what I was wanting to try but I figured trance having a lot of pumping of audio would be a good test.
I will upload future videos using rock music and other styles of music.
Anyways enjoy my video for now, it took an hour to upload because of the ADSL line which sucks.
The audio is far from perfect also because of the natural digital compression but it should give you a sense of the processor and how it sounds.
Edit: after listening the audio sounds bad but disregard that as it's a youtube video. You still get the basic point when watching the video.
Anyone know how I can record audio/video of my computers screen in high quality let me know please. For now this will do, and at least give an impression.
OH DUH my bad, simply change the youtube quality setting. It will make it sound and look good if you have the internet connection to support it. I feel like an idiot now lol. 720p is a good place to start. It helps the audio greatly also.
Still though at the best quality it still sounds like it's coming through a warm fart.
I'd appreciate ideas how I can upload quality samples. I spent way too much time on this unit to have everyone think it sounds like shit because of youtube. Thanks.
Guess the visual representation of the audio is worth it alone though. That spectrum graph really does prove a heck of a lot.
Post by jessewillem on Dec 26, 2012 12:12:25 GMT -6
I've added also some video's about my software DSP processor on YouTube. Showing of what it can do already.
I've set it up to show of the distortion cancelled clipper, so it's sounds loud. But the program can also be set up to do just leveling or just a little bit compression. Also, I still have to do much work on making a nice composite signal from it, so there gonna be lots of work to be done on the stereo generator.
Also your [Kage's] audio processor does have a nice sound ;-) My wish is to turn my processor to in a hardware box someday, but I don't think that is going to happen in the next 5 years...
This has been bugging me since I started thinking over it. Most stereo FM audio processors tie together the left and right channels gain reduction circuits so that if there is gain reduction or "limiting" on one channel it also affects the other channel even if the other channel doesn't need the gain reduced, and vise verse.
My homemade FM processor doesn't do this and instead treats both channels as complete separates. However making them tie together like that would be very easy to try and I may even experiment to see what I think of how it changes the sound.
Here's the schematic again for one channel of my processor..
I could simply tie a low value resistor across the Left and Right channels FETs gate so that G/R of either channel affects the others. Or at least I think in theory that should work without any issue.
This would be done for the first limiter and the HF limiter (separately) which is exactly how the Orban 8000 does it by looking at their schematic.
Any thoughts on this? Why tie both channels gain reduction together like that? I assume they do it to preserve the sound stage or something in music? I actually like the way my processor sounds now but hey if this simple little modification makes it sound even better then I may try it, or maybe even add a toggle switch to flip between separate or together G/R.
Post by jessewillem on Mar 19, 2013 13:10:50 GMT -6
Well, the reason why many compressors apply the same gain reduction on both channels is to prevent shifting the stereo image because one channel is more compressed than the other.
I've implemented stereo linking too in my compressor and limiting section. By calculating the gain reduction for both channels, and apply the highest one on both the channels.
Well I made the simple modification to add a jumper between the FET gates of both Left&Right first limiter stage. This properly combines the gain reduction of both audio channels without causing any audio crosstalk. Tested all and it works fine this way. In fact it doesn't affect the circuit in any noticeable way besides to do what is intended. Because I made it a jumper I can always turn on/off the combined G/R. Most music I don't notice much of any difference but with some songs that have different bass volume on either channel the sound stage does sound slightly more centered and realistic like the song does in its original form before processing.
I found combining the gates of the second (HF) limiters did nothing noticeable but did cause a few issues with sound balance so I did not even attempt to modify that and I highly doubt it would be necessary. I think Orbans processor does combine the G/R of the HF limiters but very loosely as I recall.
IIRC, those older Optimods also had a "phase chaser" circuit which would aid in correcting phase errors from analog sources like slightly out of alignment R/R decks, cart decks etc. Also there were separate phase chaser units that could be chained in on the audio line.
Not very useful these days with digital sourcing, but if your audio sources has some old tape based playback, works wonders in correcting phasing and maintaining stereo image. Better than chasing phase with a "greenie" tweaking at the head azimuth screw!
Peace!
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