Reading a spectrogram

[Dwetmaster]

While Monitoring with a spectrogram, should I allow any red at all?

[Frodo]

What do you allow when you monitor via a channel strip?

[Larry Mal]

You mean red in the spectrogram, and not in the metering, correct?

[Larry Mal]

Because a spectrogram will show contrasts in the material. So there will be red and blue no matter what the levels are. You can see this by loading up a stereo track- a commercial song or something like that- and pulling the master fader down by 20 dB. There is still the same contrast there, even though the levels are much different. Thus it will be looking for contrasts, not level, and the red in there does not correspond to overloads in level.

I think this is what you are asking about.

[Dwetmaster]

Yes Larry, I was talking about red in the spectrogtram.

So the spectrogram is only to monitor my dynamic range? What's the normal use of a spectrogram then? I guess I'll need to read on the subject a "little" bit...

[Larry Mal]

No, it's not to measure dynamic range, it's to show you where in the audio spectrum an event occurs by showing loudness as colors in a real time waterfall. Let's say you had a quiet acoustic guitar playing, then you'd see that as a relatively quiet (blue and green) waterfall in the audio region it inhabits. Then let's say a person were to yell "Hello!" You would see that as likely red in the portion of the audio spectrum in which the vocal occurred.

I can't say that I've done a lot of research as to what spectrograms exactly are and do, but thanks to my good friends at this site here, I've learned all I'll probably know for quite some time:

http://en.wikipedia.org/wiki/Spectrogram

But I'll tell you that I did the check as far as placing a stereo mixed track on a track in Logic, and put the Nugen Audio's analyzer on it, and took a look. Then I did drop it down 20 dB and the spectrogram was showing me the same information as before, so this tells me that it isn't measuring volume, per se. However, this was a two minute test, and what it would reveal on a mono track (of say a violin) I can't say.

As far as how I use it in my limited way, and I'm no expert with it, I've found it useful to check the overall coloration of a mix. It can show you quite clearly when something comes in. Try it with a song in which the vocal doesn't appear for a bit, and you'll notice that you can see right when the singer starts, as well as where she starts in the spectrum. She will be colored in red and orange, since she is likely recorded hot, and you'll see this.

This can be helpful in a mix, since you'll soon know where your singer is with greater accuracy then by using standard FFT grids, which also shows this, but a lot faster. The strength of a spectrogram is in its waterfall method, which shows things slower and in real time. You have to watch pretty carefully, but once you have attained the skill you'll find it's pretty great.

Give me a minute to find out how to put up pictures on this site- I guess I'll need to set up a Photobucket account- and I'll put up some examples while I drink beer.

[Larry Mal]

Allright, let's try it. This is Bob Dylan's Lay Lady Lay running through Nugen Audio's Visualizer. This is the beginning of it, before Bob starts singing. You'll notice a lot of yellow in the bass range, where there is always a lot of action, but it's all cool blue and whatnot in the treble.

[Larry Mal]

This is not a very hot song. This is right when Bob starts singing. You can see his vocals of "Lay lady lay..." in this photo. It's in the range of 400-500 Hz. It also is in yellow, because this is an old recording (I picked it as something you could easily hear if you don't know it) and so there is no real red in this laid back song. Anyway, when he sings a word, it shows up as a yellow blob in the waterfall around that range. He's Bob, he's not going to go much beyond that range:

[Larry Mal]

Now here is the next line, "Whatever colors you have in your mind..." is still in the 400-600Hz range. The snare has come in and is also visible as a loud, yellow blob in the waterfall.

[Larry Mal]

Anyway, I hope this helps. You can see in the third picture there is more going on in general, the song has picked up. The snare is pushing its area into the red (it's around 180 Hz), and in the treble portions of the song there is now a bit of green, which would reflect what the steel guitar and the acoustic guitar are doing- they've started playing louder is what. The kick drum is showing as the yellow blobs around 40-60 Hz. I'm guessing at some of this- I haven't made a real study of it, sorry, and it could be the bass guitar for all I know at this point. Either way, the bass. Bob's vocals on the chorus have moved up from the 400-500 Hz range to 500-600 Hz. Not a big difference, but when mixing, a spectrogram is a good way to find out how to clear space for something to sit. You are probably a better mixer than myself and have no doubt figured that out already.

Another use I have found is with the Izotope RX, in which you can see when a transient burst that is a cough occurs, and hopefully edit that part and that part only out of a busy live recording. It takes some practice, but it's worth learning if you think you'd ever want to do that. In the hands of the unskilled- people like myself- you'll get some artifacts, but you can probably get good at it over time same as anything else.

Stillwell makes a plug in that will do a similar thing for less money. But not as deep. Here it is:

http://www.stillwellaudio.com/?page_id=32

Anyway, like I say, I hope this helps. I didn't have a lot of time to put this together, and you may know a lot of this anyway. The Bob Dylan song, unfortunately, doesn't have a lot of dynamics overall. But you'll get the point. Now I have to go... beer doesn't drink itself.

[Dwetmaster]

Thanks a lot man. Cuemix already has a pretty good ( i think ) spectrogram. It's up to me to read it...