Phase prob­lems probed; up­sam­pling au­dio.

Sound & Vision - - CONTENTS - BY AL GRIF­FIN

QI can’t seem to get clear di­a­logue when play­ing some movies and TV shows and am forced to used closed cap­tion­ing. I be­lieve my prob­lem is caused by im­proper phase. My home the­ater setup con­sists of five speak­ers plus dual sub­woofers that have a po­lar­ity switch and phase knob. I’ve heard that the proper way to ad­just phase is to play a sine wave at 80 Hz (same as my cross­over set­ting) and then turn off all speak­ers ex­cept the left or right speaker and its ad­ja­cent sub. The next step: ad­just po­lar­ity and phase un­til you mea­sure the high­est SPL level at the main lis­ten­ing po­si­tion. Am I go­ing about things right? Any other sug­ges­tions to im­prove di­a­logue in­tel­li­gi­bil­ity in my sys­tem? AMIT ALCALAY / VIA EMAIL A It’s un­likely that phase prob­lems are af­fect­ing di­a­logue in­tel­li­gi­bil­ity in your sys­tem. First, the po­lar­ity/phase ad­just­ments you de­scribe are in­tended to min­i­mize fre­quency re­sponse dips in the re­gion where the main left/right speaker out­put blends with the sub­woofer’s out­put (80 Hz, in your case). Sec­ond, the fre­quency range of movie di­a­logue rarely ex­tends down to 80 Hz— even if the actor de­liv­er­ing it hap­pens to be Ving Rhames ( Mis­sion: Im­pos­si­ble, Pulp Fic­tion, etc.)— so the out­put of your sub­woofers shouldn’t af­fect di­a­logue clar­ity.

Where a phase is­sue could cre­ate prob­lems is if the speak­ers are wired in­cor­rectly. A ba­sic sys­tem check would con­firm po­lar­ity by ver­i­fy­ing that all speak­ers are wired with the pos­i­tive (red) out­put on the amplifier con­nected to the pos­i­tive in­put on the speaker, and the neg­a­tive (black) out­put con­nected to the speaker’s neg­a­tive in­put.

You could then use a test disc like Dis­ney’s WOW (avail­able from Ama­zon.com) or any Blu-ray or DVD with the THX Op­ti­mizer (I use Pixar’s Toy Story) to check for proper phase be­tween the var­i­ous speaker pairs in your sys­tem. For ex­am­ple, to eval­u­ate phase with your main left and cen­ter speak­ers, in-phase pink noise is played, fol­lowed by out-of­phase pink noise. The first tone should sound clear and fo­cused, the sec­ond dif­fuse. If the re­sults you hear are re­versed, then one speaker in the pair is wired in­cor­rectly.

Another fac­tor that can re­duce di­a­logue in­tel­li­gi­bil­ity is cen­ter-chan­nel level. Even when the cen­ter speaker’s out­put is cal­i­brated to match other speak­ers in your sys­tem, the sound­track and sound ef­fects in some movies can ob­scure di­a­logue when lis­ten­ing at a rea­son­able level. To fix this, you should tem­po­rar­ily boost cen­ter speaker level for cer­tain con­tent. Another op­tion if your receiver pro­vides it is to use a dy­namic range com­pres­sion mode such as Audyssey’s Dy­namic EQ/ Dy­namic Vol­ume or THX Loud­ness Plus that works to main­tain a con­sis­tent level among all sur­round chan­nels at var­i­ous vol­ume set­tings. Q When re­search­ing DACS, I ran across the Cam­bridge Au­dio CXN, a net­work au­dio player that up­sam­ples all in­puts to a 24-bit/384khz hi-res for­mat us­ing “poly­no­mial curve fit­ting in­ter­po­la­tion.” This seems to be the only DAC that of­fers that kind of feature. Most Ul­tra HDTVS and Blu-ray play­ers also pro­vide up­scal­ing, but for video. In my ex­pe­ri­ence, this is a very ef­fec­tive feature that im­proves the ex­pe­ri­ence of watch­ing a reg­u­lar DVD. Here’s my ques­tion: Does au­dio up­sam­pling have the same ef­fect as video up­scal­ing? MIKE YANG / VIA EMAIL A Many au­dio DACS per­form some type of up­sam­pling or over­sam­pling be­fore con­vert­ing the dig­i­tal bit­stream to ana­log for­mat. Ac­cord­ing to Cam­bridge Au­dio, what’s dif­fer­ent about the up­sam­pling tech­nol­ogy used in its CXN is that an al­go­rithm in­ter­po­lates au­dio data with greater pre­ci­sion than stan­dard sam­ple-rate con­ver­tors can de­liver, cre­at­ing

a curved wave­form that more closely ap­prox­i­mates the orig­i­nal ana­log au­dio sig­nal. Other ben­e­fits it cites for the CXN in­clude a re­duc­tion in jit­ter dis­tor­tion and an abil­ity to ap­ply pro­cess­ing to all in­puts, in­clud­ing com­pressed streamed sources like Spo­tify.

Au­dio up­sam­pling is in many ways sim­i­lar to the scal­ing that hap­pens with Ul­tra HDTVS and Blu-ray play­ers. For video, how­ever, the pro­cess­ing gen­er­ates new im­age pix­els in­stead of con­vert­ing au­dio sam­ples.

With most high-qual­ity video scal­ing so­lu­tions, an al­go­rithm scales the orig­i­nal im­age data us­ing a com­bi­na­tion of noise re­duc­tion, pixel in­ter­po­la­tion (to ren­der smooth, jaggy-free edges), and fine con­trast and de­tail en­hance­ment. As you’ve con­firmed with your own eyes, the re­sults can look very good. On the au­dio side, prod­ucts like Cary Au­dio’s AIOS, an up­sam­pling in­te­grated amplifier/dac that de­liv­ered im­pres­sive per­for­mance when Sound & Vi­sion tested it in 2017 (see soun­dand­vi­sion.com), con­firm that au­dio up­scal­ing can also have a ben­e­fi­cial ef­fect.

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