8.The design constraints for MultEQ were that it
(a) must fit within a small portion of the DSP so that other processes can also run and
(b) it must use FIR filters because of the well-known artifacts that IIR filters cause particularly in the time domain response.
As it turns out, these two requirements are contradicting. In order for FIR filters to be effective and capable of correcting to low frequencies,
they must consist of several thousand coefficients (taps). The problem is that the CPU power required increases with the number of taps,
hence the dilemma. What we did at Audyssey was to come up with a different way to partition the frequency axis so that
we can use fewer taps and yet not completely give up on low frequency resolution (and therefore low frequency correction).
This allows us to take a 512 tap filter that would normally have a resolution of 94 Hz (meaning that any peak or dip narrower than 94 Hz would be missed)
and significantly improve its resolving power. The resolution of the filter actually varies continuously with frequency and starts at around 10 Hz.
Does this mean that MultEQ can correct an arbitrarily narrow peak or dip at 30 Hz?
Of course not. The reality is that in the MultEQ XT version found in receivers, we can correct broader features below 100 Hz better than narrow ones.
For example, a lump that is half an octave wide at 50 Hz can be fixed. A narrow dip or peak that is 1/3 or 1/6 octaves wide and
centered at 30 Hz will be improved, but not eliminated. (以上晶片技術問題原文)
原文如下:
A good guideline is to look up the frequency response of your speaker and find its lowest frequency (or the point where it drops off -3dB),
then add about 20Hz to that to use as the crossover setting. That said, the crossover's slope (i.e. how quickly it transitions) is pretty steep,
so you might be able to get away with adding as little as 10Hz to your speaker's lowest reproduceable frequency. Start with 20,
then tweak to preference to get the best transition.
9.我應該改變 Audyssey 所測的喇叭距離嗎?
Audyssey 似乎可以偵測喇叭距離與實際距離相當接近，但有些人仍認為這不是喇叭中間音像最佳設定。你可以用 Digital Video Essentials 測試碟中一系列測試音（這些測試音音場都是在喇叭正中央），
一次改變設定距離約半英呎慢慢感覺音場聚集在中央（意即在這樣設定下喇叭相位正確）。如果聲音變得越分散或者難以聚焦，那表示改變距離設定後讓喇叭與其他喇叭相位不正確了。
While Audyssey does seem to properly detect speaker distances close to their actual physical distances,
some have found that this is not the best setting for between-speaker imaging.
The calibration disc has a series of test tones that are placed equally between channels.
Using these tones, you can tweak speaker distance a half-foot up and down to listen for the setting that makes the sound "hang" in space between
the speakers (which means it is in phase at that setting).
If the sound becomes more diffuse or harder to pinpoint, it is because changing the setting is putting it out of phase with the other speaker.
要改變喇叭距離設定、面對前牆依照下列步驟去做：
a.在前左聲道與中央聲道播放特定頻率測試音、然後一點點慢慢改變設定值前後移動中央聲道、看看是否在某距離設定時、讓你感覺聲音更聚焦在兩支喇叭中間！
然後在前右聲道與中央聲道重複這動作，選擇一個讓兩邊聲道聽起來最佳的設定值作為中央聲道距離設定值。
b.在右前聲道與右環繞聲道中間播放測試音頻，然後上下調節右環繞喇叭距離，找出側牆喇叭距離的最佳位置，因為環繞聲道位置通常高於主聲道喇叭、
或許無法找到一個完美的設定，但你應該可以找到一個從側方向來較佳的音場位置！
c.重複 b 的動作在左環繞部份，如果你只有 5.1 配置、那到這裡你就完成設定了。
d.For 6.1/7.1 setups, put your receiver into DPL-IIx Movie mode and play the tone between the right surround and the rear surround
(since DVE only has 6.1 tones), or change DVE to the DTS track and use DTS-ES Matrix mode,
then bump right rear surround distance up and down slightly until you hear solid placement of the sound between the two.
Then repeat using the tone between left surround and rear surround, changing the distance setting for the left rear surround.
If you only have 6.1, bump your rear up and down to listen for the setting that works best with both tones.
10.為什麼重低音的峰值切削設定如此低?
一個人們常犯的錯誤是把重低音的增益或音量調太高了、如此一來重低音的哼聲與躁聲被放大了。
如果 Audyssey 把 subwoofer trim 設定的很低、請嘗試將重低音的增益或音量降低然後再測一次！或者你也可以用 SPL meter 檢查一次、這樣你就不用 Audyssey 流程重跑一次。
理想上 subwoofer trim 儘可能接近 0、而此時你的重低音 gain 在其最大 1/3 處！
11.為什麼我的所有聲道 TRIM 值都很低?
Audyssey 試圖讓所有喇叭在你的擴大機相對音量值調在 0 時、你聽到是參考播放音量值 reference playback level (也就是說你的喇叭此時音壓 105db，重低音音壓115db)
但是因為各廠喇叭效率不同，這些音壓強度會因為喇叭廠牌、房間音響效應、等等因素而改變。如果你不在乎 0 是參考播放音壓或者是你用絕對音量讀數、
那你可以把所有聲道值等量提高到接近 0 如果你喜歡地話。
然而因為 ONKYO 705 的最大音量值是決定於你所設定的 maximum channel trim，如果你設定 highest channel trim +2、那最大音量會從相對音量 +18 減到 +16。
因此你不會因此從擴大機得到額外輸出音量！很多人可能注意到 Audyssey 設定 TRIM 值低約 2-3dB 來達到 reference level at 0。
你可用 SPL meter 再測一次調整各聲道道音壓值到 75db。
14.Why can't I tweak the EQ settings that Audyssey comes up with? (針對ONKYO 705)
While the 705 offers a 7-band manual EQ, this is only as a convenience and does not reflect what MultEQ XT uses to make its adjustments,
nor does it account for adjustments in the time domain that Audyssey makes. For each channel, Audyssey bases its equalization on hundreds
of points along the frequency range and can potentially be making as many adjustments per channel.
There is currently no way to alter those settings or even represent them on-screen, even with the vastly more expensive MultEQ XT Pro that
uses a standalone PC to do its calculations.
15. But if that's true, why does X brand let you change the EQ after Audyssey?
Some receivers, notably the Denons, let you alter equalization after Audyssey runs.
They do this by copying the resulting curve as best they can to the 7-band EQ, giving you a general notion of where the biggest problems lie.
This lets you make coarse adjustments but also negates all the fine adjustments that Audyssey makes, as well as the ideal equalization for all positions.
7 bands of equalization in no way represent the resolution with which Audyssey makes its adjustments.
17.如果測出來的低頻分頻點是 80HZ 而我的喇叭設定分頻點是高於這值、這中間的聲音會不見嗎?
低頻分頻點只影響重低音輸出聲道(the .1) 不是整體聲音
The 705 defaults to the THX LFE cutoff of 80Hz and Audyssey doesn't adjust that setting.
However, the LFE channel by its very nature is brickwall filtered during encoding at 120Hz. If you want to accurately reproduce the entire LFE channel,
set LFE cutoff to 120Hz. However, few sound mixes have audio above 80Hz in the LFE channel, which is why THX recommends the 80Hz cutoff.
Also, because the LFE channel receives a +10dB boost during decoding, the THX recommended 80Hz cutoff is there
to reduce the chance of humming/noise above 80Hz from the LFE channel. Chances are that you will not notice a significant difference,
if any, by changing LFE cutoff from its default of 80Hz, but doing so has no effect on the bass redirected from the other channels.
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