Benefits of Using Proper Digital LevelsI was browsing some various message boards recently, and ran across a post titled “The Reason Most ITB Mixes Don’t Sound as Good as Analog Mixes.” If you’re anything like me, this is probably very intriguing to you. I realized almost immediately after starting to mix on an analog board (first my Soundcraft Ghost 32 LE) that my mixes sounded more open, deep, and punchy than when I had mixed solely in Pro Tools. It could be argued that my mixing skills had improved, but I remember very distinctly the first mix that I did on the Ghost just having a different “sound” and more life to it (this was a remix of a song that I had originally mixed in Pro Tools).
There are endless discussions and debates that can be found all around the web regarding mixing ITB vs. OTB, using a console vs. a summing box, and everything in between. Personally, I really like using a console, but as far as I’m concerned, you can’t beat the instant recall-ability of doing things ITB. For me, however, it comes down to sound, and in my experience, external summing on a board just sounds so much better than Pro Tools summing that I’m willing to put up with having to take great care to document all of my settings in order to recall mixes.
I don’t want to get too far off the subject, so with all that being said, here is a one sentence summary of the very, very long thread (87 pages as of this post!) that I mentioned above: when tracking to a DAW at 24 bit, LOWER YOUR TRACKING LEVELS! Before you scream that this goes against the basic fundamentals that you learned about recording, let me explain the basic principles behind it, and it should all come together and make sense.
First off, this is just going to be a summary, and I highly recommend that you read at least the very first post of the thread by Skip Burrows, Chief Engineer of Sunrise Sound Studios in Houston, TX (a link to the thread can be found at the end of this post). In the days of all analog recording, it was very important to hit tape machines at a level hot enough to get signals sufficiently above the noise floor of tape. Generally (with some exceptions), it was a good idea to try and record with levels around 0 on the machine’s VU meters. The difference between VU meters found on analog gear the meters in DAWs is that VU meters show RMS value, which is an average, while DAW meters indicate peak value. The needles on the VUs were too slow to respond to sharp transients, such as snare drums attacks, which could potentially peak ten or more dB over 0VU. Most well designed analog gear has a certain amount of headroom over 0VU, after which the audio signal starts to become considerably degraded. Herein lies the problem: you must reference 0VU and 0dBFS (the top of the DAW meter) to a common value.
In the analog domain, 0VU = +4 dBu (which also = 1.23 volts). Looking at the specs on an SSL AWS900+ for reference, it says the headroom is <+27 dBu. Since 0VU = +4 dBu, this console has about 23 dB of headroom above 0VU (27dB – 4 dB) before the signal is shot, and this amount of headroom is similar to most well designed recording consoles. In DAWs, the top of the meter, 0dBFS, is the maximum amount possible – there is no headroom above it. So when you record with your signals peaking towards the top of the meter, it’s like running an analog board with the VUs constantly pegged! What this means is that when tracking to a DAW, the rms level should be around -20 dB on the meters, with peaks no higher than -6 dB (peaking no higher than -6 dB alleviates the potential for intersample peaks, which could be the subject of an entire other article). Many will argue that this is not the best practice because you need to get the signal as high as possible above the noise floor. However, since 24 bit recording yields a noise floor of -139 dBFS, keeping the meters around -20 dBFS still yields a range of almost 120 dB! Using the SSL AWS900+ once again as a reference, its noise floor is only about -80 dB below +4 dBu, so you can see that a noise floor of -120 dB will be more than enough.
Now, there is also the issue of what to do with digital sessions that have already been tracked very hot. If you’re going to be splitting the tracks out to a console, then you’ll most likely be adjusting the line trims on the board so that the tracks are hitting the needles at an appropriate level. This will not only make the console perform better, but also all the analog gear your using, as you’re hitting it closer to the +4 dBu level it was designed to work around. However, this does not help if you’re mixing solely ITB or if you are using lots of plugins on the tracks before you hit the console. Believe it or not, plugins are designed to operate at the same reference level as physical equipment. If you want to see this illustrated, try inserting a Waves SSL Channel on a snare track, and click on the snare preset. You will see that you have no headroom left and that the plugin, as well as the track, is probably clipping.
In order to remedy this, try placing a trim plugin as the first insert and trimming the tracks down anywhere from 10 to 20 db. This will give you sufficient headroom for all of your plugins and effects ITB, as well as any outboard gear that you may be using either via a console or as hardware inserts. Try this out and let me know what you think! I could immediately tell a difference in my mixes when they had a little more room to breath, and it’s nice not to have to worry so much about clipping occurring in plugins where it may not be easy to see.