When I got some of my tracks mastered recently, the engineer was using this Diamond TDM bundle, and one of his plug-ins was this stereo phase analyser. It had a little circle in the middle, and then in 360 degrees around it sound waves were animated fluctuating all over the place.

He said that he was checking for phase problems. If there are phase problems, what does this mean - and how does he solve them?

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DJ/Producer/Creative Entrepreneur

phase problems basically occur when the waves in the left and right signals in a stereo signal principally get out of sync (way over simplified but its an effective illustration).

in a worst case scenario they can cancel each other out entirely (an effective studio tool) but in more practical terms cause an imbalance in the perceived energy of the song.
the brain can be very good at spotting this with the effect that a song can sound lopsided even with both left and right channels at exactly the same volume.

over use of stereo width creation plugins or effects can create the problems highlighted above by shifting sounds with a wide image already into this realm.
similarly delays can also cause the same effect of phase problems and another very common source is recordings made with a stereo mic.

in todays world of digital media and CDs, phase problems in a final track, especially momentary occurences can easily be left so long as they do not create a feeling of incorrect balance or an obviously audible negative impact on the music however if pressing onto vinyl they can cause the needle to jump out of the groove and thus render a recording useless if serious enough.

a check is used in nearly all mastering applications to point out potential problems within a source material, i use it without fail, however appearance of such artifacts does not always mean that theres something terminal within a mix or the recording process

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high quality audio mastering for vinyl and cd.
point one mastering

sorry forgot the reply to the second part.
a simple way to rectify is to just narrow the stereo width slightly until it is no longer an issue and is within normal parameters.

there are much more complicated and transparent methods however if i told you that im afraid id end up rapidly out of a job.

you need to be practised in the black arts for that info

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high quality audio mastering for vinyl and cd.
point one mastering

Nice!

Tell me your black arts. I wont tell anyone - besides, it's how you do it, not what you know. I could read a book on the secrets of football, but that wouldn't mean I could play as well as Arjen Robben when I got on a pitch.

:-)

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DJ/Producer/Creative Entrepreneur

Quote neilwight:

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... however if pressing onto vinyl they can cause the needle to jump out of the groove and thus render a recording useless if serious enough.

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Just to add a bit more on that - I *think* (but I could be wrong) that the reason for this is that vinyl is encoded using mid/side, so the sideways waggle of the groove carries the mid info and the up/down depth waggle of the groove carries side.

If there's a bass signal that's out of phase between left and right, that's going to result in a very strong side signal, thus a very waggly depth groove that could throw the needle of the record player (or even the cutting lathe).

In most records the strongest and bassiest parts of the signal are kept in the middle, so they're only enocded on the sideways waggle of the groove, not the depth.

Another prob with phase, on any medium, is mono compatibility. If left and right are out of phase, then if the track is played back in mono, they'll cancel each other out, so you'll lose bits of the original signal.

Matt

Quote Matt Downing:

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Quote neilwight:

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... however if pressing onto vinyl they can cause the needle to jump out of the groove and thus render a recording useless if serious enough.

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Just to add a bit more on that - I *think* (but I could be wrong) that the reason for this is that vinyl is encoded using mid/side, so the sideways waggle of the groove carries the mid info and the up/down depth waggle of the groove carries side.

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If I was being pedantic then I'd say that vinyl is actually cut with each groove wall carrying one channel. This effectively works in the way that Matt describes - a mono signal gives only horizontal movement but the cutting stylus is driven by two sources at 45 degrees to vertical.

Cheers.

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Quote James Perrett:

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If I was being pedantic then I'd say that vinyl is actually cut with each groove wall carrying one channel. This effectively works in the way that Matt describes - a mono signal gives only horizontal movement but the cutting stylus is driven by two sources at 45 degrees to vertical.

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True, the cutter heads of most (if not all) lathes do operate with the motor assemblies driving at 45 degrees to the vertical, and the groove side walls represent the left and right channels. And Matt is also correct in that the side component of the stsreo signal is vertical, and thus significant S signals can cause major tracking issues.

Hence serious phase issues, where the S component of the stereo signal becomes excessive, are one of the things that mastering (and recording) engineers like to watch out for.

As has been said, not only can this kind of problem make it impossible to cut a vinyl record, but it can also result in parts of the mix disappearing when auditioned in mono.

Radioplay is made even more complicated because a lot of radio transmission processors incorporate a 'phase rotator' which adds further phase shifts in order to be able to increase perceived loudness.

The phase meter display you mention is an increasingly common way of assessing a stereo image. Essentially, the left channel is shown on an axis that runs from 10.30 to 4.30 (if you can imagine a clock face), and the right channel runs on an axis from 1.30 to 7.30.

A mono signal will therefore produce a vertical line, and a normal stereo signal will be a circular ball of jumbled lines. IF the ball looks squashed -- wider than it is tall -- there may be phase issues to deal with.

Often, the problem can be fixed by reducing stereo width for only a select band of frquencies -- it's very common, for example, to narrow the bass region, while leaving the width of the mid and high bands as normal.

hugh

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Technical Editor, Sound On Sound