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Whether one is producing music, podcasts, game sounds, or film sound effects, Digital Audio Principles provides the tips and techniques that will make the project a success. Author Dave Schroeder explains the basics of digital audio production techniques and covers the essential hardware and software. He also discusses sound theory, frequency response, the range of human hearing, and dynamic range.
So, let's talk about a few other considerations to keep in mind when you're dealing with audio file compression. Now generally speaking, lossy compression doesn't do so well with the higher frequencies when you have to use lower bit rates. When I say lower bit rates, I am thinking about rates below that magic combination of 128 kilobits per second, matched with a sample rate of 44.1 kHz. You'll notice that if you start to apply rates lower than this, you might get something like a searing sound on some of the higher frequencies or quicker transients, things like vocals and symbols.
I call it a searing sound, it's like if you think about you sear some ahi tuna and throw it on a hot pan, there's that sizzling, searing sound, and you know it when you hear it, because you don't really want to listen to it. Sometimes you'll listen to some voices that are compressed too much, and you'll have to hear that, and you usually end up turning it off because that's little searing sizzle in there it's just enough to make it uncomfortable, or annoying to listen to. So, the first thing to do is generate a file at that rate you want to use, and just listen back and see if you have trouble with some of these higher frequencies, and if there's a little bit of that searing sound.
Now if there isn't, you are in the money, and you can just go with it. But if there is, there are a couple things you can do. The obvious solution is to go ahead and increase the bit rate. Chances are, at 128 kilobits per second, you won't notice these kinds of searing artifacts at all. But if you know you have to use a low bit rate because you have to meet a certain target file size, there's something you can do to try and improve the sound a little bit and get rid of that searing quality. This involves cutting some of the high frequency material before you apply the file compression. Now I know this is hard to stomach, because you've been working for a long time on this thing and producing it, trying to make it sound good, and doctoring the EQ, and just really trying to make it sound sonically even, and now we are going to go ahead and actually chop some of that off and basically undo some of your work.
But we have to remember our objective, and that's to create listenable audio. We might generate a great sounding production, but then if we compress and it sounds lousy and send it out there, people aren't really going to want to listen to it, or they are not going to be as attentive to it as we want them to be. We want something that people are happy to listen to and not distracted by the sound quality. They are more interested in the content. They want to hear if that's a great song, or they want to hear who you're interviewing in that podcast. So remember that we're always trying to make listenable audio. So what I like to do is I take my final, mastered file, whether it's stereo or mono, you can go and go in and make a few different copies of that file and then start applying different EQ to these different files.
We want to reduce the high-end. So you can do one where you just shelve most of the high-end down a little bit, and you're just turning it down a little bit. Then you can do a few where you use a high cut and cut off things at different frequencies. Maybe do a cut at 16K, maybe one at 12K, and then another version with a cut at 8K, so that you have three or four different files that have the high frequencies lopped off the top, more or less. Generally, it's always a good idea to generate a few different masters, with different EQ cuts on them like this, so that if somewhere down the road it comes up that you need to compress things at different rates, you have files ready to go, and you don't need to go back in and open up sessions.
But always remember, regardless of what you're doing with EQ and rates and math, and whatever you're working with to come up with these files, it's always best to give them a listen and trust your ears. Your ears will help you determine what sounds good enough and what doesn't.
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