Ableton Live Tutorial – Better Sound with Hi-Quality EQ8
More info – http://bit.ly/w4n2mS
In our new Ableton Live video tutorial series, “Did You Know?”, Ableton Certified Trainer, Dubspot Instructor, and electronic musician Thavius Beck checks out less explored and slightly hidden features in Live. In this newest installment of Did You Know?, Thavius explains and demonstrates an often overlooked an even more often misunderstood feature; Hi-Quality mode on the EQ8.
The EQ8 has a Hi-Quality setting that is not enabled by default. We are able to find the Hi-Quality setting by right-clicking on the EQ8′s title bar and selecting “Hi-Quality” from the contextual menu that appears. Once that has been done, the EQ8 will be in Hi-Quality mode, but what exactly does that mean?
This is a question that took me quite a bit of investigation to find the answer to, and one that requires more explanation than I intended for these particular videos, but this series is all about sharing esoteric knowledge (as it relates to Live of course) so that is what I will do right now.
When Hi-Quality mode is enabled on the EQ8, the audio being fed into the EQ is oversampled by a factor of 2 (meaning the sample rate of the audio is doubled. If your session’s sample rate is 44.1kHz, enabling Hi-Quality will make the audio being fed into the EQ8 88.2kHz). Then the EQ changes are calculated at the doubled sample rate, and finally the audio as it leaves the EQ is undersampled by a factor of 2, or basically brought back to it’s original sample rate.
Why does this happen? It all has something to do with what is referred to as the Nyquist Point. The Nyquist Point is one half of your sample rate, so if your session’s sample rate is 44.1kHz, the Nyquist Point will be 22.05kHz, which is right at the upper limit of human hearing, and just beyond the furthest right edge of our EQ8′s GUI. Any audio that produces a frequency higher than the Nyquist Point cannot be accurately reproduced digitally and will have aliasing or digital distortion as a result.
Because of this, the EQ8′s frequency range was initially limited to 22kHz on the high end (when working on a session with a 44.1kHz sample rate). If your EQ is in normal mode (not Hi-Quality), and you create a notch on the 4th EQ point (reduce the gain all the way on the 4th point), start to increase the Frequency on that 4th point. You’ll notice that as you get closer to the Nyquist Point (22kHz when working with a 44.1kHz sample rate), the curve of the EQ gets squashed so that the curve doesn’t extend beyond 22kHz. Now, enable Hi-Quality mode and try the same thing. Notice how the EQ curve remains intact no matter how close you get to the Nyquist point.
So what does this mean in terms of practical application? Well, it means that you will probably only notice the effect of the Hi-Quality EQ8 if you’re working on a session with a 44.1kHz sample rate, and the improvement will really only be noticeable on the higher frequency sounds effected by the Hi-Quality EQ8. As for specific instances for when you’d want to use the Hi-Quality setting and not, I think that is really for the individual to research a bit further, do a few A/B comparisons, and decide for themselves.
As I was doing my research for this post, I searched a few forums to help me gather the info I needed, and I also reached out directly to the Ableton HQ. Here is a very helpful and informative series of posts from the Ableton forums.
And below is the explanation for the Hi-Quality setting directly from Matt Jackson at Ableton HQ:
“The main difference is that the entire signal is oversampled in high quality mode. Actually the slope isn’t changed.
To get technical, in normal mode with a project sampling rate of 44.1kHZ, you have a nyquist frequency of around 22kHZ, the limit of the EQ. Because – in the design process – the filter is derived from an analog prototype, which has no such a limit, all frequencies (and up to infinity) must be matched to the available frequency range of the digital filter, resulting in the squashed slope near nyquist frequency.
If you look at the EQ in normal mode, you’ll see the filter slopes warp as they get very close to the 22kHZ mark. If you change your project sampling rate to 88.2 or higher, you’ll see that this warping no longer happens.
This is because the nyquist frequency is now much higher than 22kHZ.
The same thing happens when you turn on high quality mode when working at 44.1kHZ. Then Live over samples just the EQ so that the filter gives the correct response all the way to the end. (There is no change in the bottom.)”