Wonderful width
It’s possible to create wide and spacious sounding mixes that also work in mono – but it doesn’t happen by accident
The Haas delay trick is fairly well known: add a delay of less than about 30ms, and pan it to the opposite side of the mix. With such a short delay time we won’t hear it as a discrete echo: instead, our brains interpret it as a reflection from a wall, and the part will gain a lovely sense of depth and dimension.
The method often recommended is to duplicate the part, then slide the duplicate back a few ms on the timeline to create the delay. We don’t recommend this method, however, as its difficult to tweak the delay time while listening, and this is important if you want to preserve mono compatibility. Unfortunately, when you listen in mono, the two signals will add together and cause comb filtering: the characteristic pattern of boosts and notches shown in the images.
How big a problem this is depends on the part. If it’s just background texturing, it might not matter too much. But if the part is critical to the song, like a rhythm guitar, you wouldn’t want it to sound really weird and ‘phasey’ in mono – mono still matters!
Haas it come to this?
There are two things we can do to improve the situation. First of all, the delay can be much quieter than the dry signal, yet still create a useful sense of space. Turning the delay down will result in a series of gentle ripples instead of severe boosts and notches.
And second, we can carefully tune the delay time to create comb filtering that flatters the source and helps it fit in the mix. This means listening carefully to the part in mono, and in context with the rest of the mix, as you tune the delay in tiny increments. It might take a while to find a good setting, but it’s worth the effort!
This is why we don’t recommend slipping a copy earlier in time on your DAW’s timeline: it’s much easier to tune the delay time with a plugin (like the free Sound Delay from Voxengo). Start with a very short delay of around 1ms, and set the delay signal about 3dB quieter than the dry. This will put the lowest cut at around 500Hz, a region which often gets congested in mono. Short Haas delays can add just as great a sense of space as longer times when in stereo, so short settings of around 1ms can be very useful.
Notice that the signal is boosted below the lowest cut, like a low shelf. This is more likely to be an issue with shorter delays like this, which put the lowest notch in the low-mid region. Optionally, remove the lowest frequencies of the delay with a high-pass filter to reduce the shelf.
Now gradually increase the delay time while listening carefully to the mono mix. Tiny changes make a significant difference to the resulting comb filtering. Try tweaking in increments of 0.1ms, or even less, and listen out for a setting that helps the part to sit better in the mix and reduces clutter and congestion.
When your delay time reaches 10ms, the lowest notch will be at 50Hz (assuming you’ve not added a high-pass filter), and the cuts and boosts in the midrange will be quite tightly spaced. Up in the treble, they’re too close to see separately on this scale. Optionally, flatten out the treble by low-pass filtering the delay, and restrict your shaping to the critical midrange.
With longer delays, the filtering becomes very closely spaced, and less useful for shaping your mono balance, so focus mostly on the range between 1 and 10ms. If you’re struggling to find a good setting, you may need to tweak the delay level; if every setting you try sounds coloured and phasey, you’ve probably got too much of the delay mixed in.
When you find a good setting, verify it by toggling mute on the delay to make sure it really does improve the mono mix. Then switch back to stereo, and enjoy the extra width and depth you’ve created!