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Message: [QUOTE="Queen, post: 90628, member: 27"] Mid is half of left plus right, side is half of left minus right, and any mono fold-down discards the side channel completely. That is the whole matrix. Two sums, one subtraction, and a set of consequences most people never work through. Mid-side EQ gets sold as a width tool. It is really a rebalancing of two signals you derived from the ones you actually have, and the arithmetic runs in both directions. So every side-channel move is partly a bet on how people will hear the record. Sometimes that bet is fine. Sometimes it quietly guts the thing you spent a week getting right. [HEADING=2]A side boost and a mid cut are not the same move[/HEADING] Both make a mix sound wider. Boost the side channel by 2 dB or cut the mid channel by 2 dB and the ratio between them shifts by the same amount. On a spectrum display, they look like cousins. In the mix they are nothing alike. A side boost adds energy, raises your overall level, and leaves the center exactly as it was. It costs headroom, and it disappears the moment anything sums to mono. A mid cut takes energy out of the middle instead. Lead vocal, kick, snare, and bass all live there, because anything panned dead center exists only in the mid signal. Cut it, and you have EQ'd your vocal without opening the vocal channel. It also helps to know what a side boost is actually lifting. Above 8 kHz, the side channel is mostly cymbal decay, reverb returns, and the tails of wide guitars. You are raising the air around the mix rather than the sources in it, which is often what you wanted anyway. Most of the time the boost is the safer instrument. Add a little side, pull the output trim back to match, and compare. If the result needs more than about 2 dB, the problem is in the mix, not the master. [HEADING=2]The low end is where mid-side EQ turns dangerous[/HEADING] Below roughly 150 Hz, most of what sits in your side channel is not music. It is room, reverb tails, and small timing differences between two microphones. Boosting it with a low shelf amplifies exactly that. Vinyl punishes this harder than anything else. Out-of-phase low frequency forces the cutting stylus to move vertically as well as laterally. That widens the groove, cuts your playing time, and can leave a groove some cartridges cannot track. Cutting engineers have dealt with it the same way for decades. The stereo field gets narrowed from around 300 Hz down, reaching full mono somewhere between 150 and 120 Hz. Exact numbers depend on how bass-heavy the material is. Digital is more forgiving, but not immune. Use the side low shelf for cuts and leave the boosts to the mid channel, where the energy stays where your listeners can find it. [HEADING=2]Mono fold-down is still a real playback condition[/HEADING] Phone speakers, most Bluetooth boxes, and a lot of club and bar systems sum to mono. So does the far corner of any room where one speaker dominates. [B]Stereo width that survives a mono sum[/B] is worth more than width that looks impressive on a meter. That correlation meter is still the fastest check you have. It reads plus one when the channels are identical, zero when they are unrelated, and minus one for a polarity-inverted copy. Watch it while you move a side shelf and you will see how quickly two decibels drags it down. Then do the cruder test. Sum to mono and listen for what goes missing, because if the hook only lands in stereo, the balance underneath it is wrong. Fix that in the mix rather than propping it up with a side boost. There is a data cost too. Lossy encoders frequently code stereo as mid and side internally. Heavily boosted side content spends bits that could have gone to the parts people actually hear. None of this makes the technique bad. It makes it a finishing move rather than a fixing move. The hardware BAX EQ has had no mid-side switch since it appeared in 2010, and mastering engineers used it happily anyway. [B][URL='https://goldmidi.com/community/threads/dangerous-music-and-acustica-audio-built-the-bax-eq-plug-in.76016/']A mid-side mode the hardware never had[/URL][/B] is a software-era addition, and additions like that get overused precisely because they cost nothing to switch on. Set the mid channel first, in stereo, until the balance is right. Only then decide whether the sides need anything at all. [/QUOTE]

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