filters and phase shift

Discussion in 'Mastering' started by Michael Fossenkemper, Jul 26, 2005.

  1. Michael Fossenkemper

    Michael Fossenkemper Distinguished past mastering moderator Well-Known Member

    I just mastered a 5.1 live concert for DVD-V. In the mains I filtered out some low rumble but left the LFE alone as there was content in there that needed to be, using analog outboard gear. When I applied the filters to the mains, I noticed that the sub sounded disconnected from the mains. I kicked in bass management and the low end goes bye bye. Ahh, the filters phase shifted the program. Anyway, this got me thinking about absolute phase in regards to material and if using things like filters which can have radical phase shifts might be doing some serious damage in regards to the absolute phase of the material. I never really think about absolute phase much when I kick in a filter. I guess it's because I mostly use a linear phase eq when I do this.

    Do any of you think about this when using analog gear
     
  2. JerryTubb

    JerryTubb Guest

    Hey Mike,

    Was it the sample delay of the ADC, post analog path, in the mains ?

    Was there an L2 connected to the path?

    We do quite a bit of DVD-V 5.1, and always carefully check (and compensate for) the delay from any processing, digital or analog, for phase issues.
     
  3. Michael Fossenkemper

    Michael Fossenkemper Distinguished past mastering moderator Well-Known Member

    There were no delay issues as far as processing. At first I tried running everything analog even the lfe, same gear on all tracks. it was definately a phase shift on the mains because when i bypassed just the filters on the mains, the problem went away. Then I tried it with plugins, same plugs accross all the tracks, even the LFE, when I rolled out the bottom on the mains, same problem just not quite as bad. the problem is that some of the same material like the kick and bass were mixed into the lfe and any phasey processing altered that relationship. I ended up not filtering any of the mains because the only thing that worked was the waves linear eq and I didn't like the way it sounded, so I just left the rumble in and used a shelf instead to lower it a bit, the rolloff was just to much phase shift. Again it was only really noticeable with bass management, unfortunately that's how most home systems work.
     
  4. dpd

    dpd Active Member

    Was it a polarity shift (an inversion) or just the natural phase shift of the analog filter? It's amazing to hear the effect of a high pass filter on bass notes. The cutoff change can literally be at a sub-sonic frequency, yet one can clearly hear the effect of the phase.
     

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