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發表於 2017-9-17 23:26:27
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<< Distortion Graph in Room EQ Wizard >> (v5.16 H
花了時間翻譯, 有興趣請參考!
By default the plot shows the actual SPL levels of the fundamental and the harmonics.
REW預設的 distortion圖表顯示為基頻與諧波的實際音壓值.
If Plot normalised to fundamental is selected the harmonics are divided by the fundamental to show their relative level and the fundamental appears as a flat line at 0 dB.
選擇 " lot normalised to fundamental" (圖表隨基頻標準化) 時, 諧波將除以基頻以顯示其相對量, 此時基頻顯示於 0dB 呈一直線.
The legend value for the fundamental will continue to show the actual SPL, the readings for the harmonics and THD will depend on the Distortion Figures setting.
基頻的圖示值將以實際音壓值顯示, 各諧波與THD讀數則依照 "Distortion Figures" 的設定.
Normalising the plot will cause the distortion traces to rise at high frequencies if the response of the system being measured rolls off (as is usually the case). This is exaggerated if Use harmonic frequency as ref is selected (see next section).
假設在高頻響應衰減的一般常見情況, "lot normalised to fundamental" 將導致高頻段 distortion 曲線升高.
此情況下將使得選擇"Use harmonic frequency as ref "(以諧波頻率為參考值)的曲線被誇大.
The boosting due to low fundamental level can be controlled by selecting Limit norm. to 30 dB below peak, this sets a lower limit on the fundamental that is 30 dB below the peak level of the fundamental - for example, if the peak of the fundamental were 95 dB the minimum level used for normalising would be 65 dB.
在基頻數值過低情況下可能導致數值增高, 此時可選 "Limit norm to 30 dB below peak"來稍作控制.
..
By default the harmonic and THD plots in normalised mode use the level at the fundamental for each frequency as their reference
- for example, the distortion figures for each harmonic at 1 kHz will depend on the level of the fundamental at 1 kHz.
預設的 "lot normalised to fundamental" 模式, 使用該基頻音壓值當作參考值.
以下舉 1kHz 作為基頻來舉例說明.
在每個1kHz 的諧波失真數值是取決於1kHz這個基頻的音壓值.
If Use harmonic frequency as ref is selected the reference will be the frequency of the harmonic
- for example, at 1 kHz the 2nd harmonic figure will depend on the level of the fundamental at 2 kHz, the 3rd harmonic will depend on the level of the fundamental at 3 kHz and so on.
(This follows a recommendation made by Steve F. Temme in "How to graph distortion measurements" presented at the 94th AES convention in March 1993. )
If the response of the system being measured is flat this makes no difference to the results, but when the response is not flat (as for most acoustic measurements) it can remove the influence of the loudspeakers fundamental response from the distortion figures.
但假如勾選 "Use harmonic freg as ref" 這個選項, 參考值則是以該諧波的頻率為準.
舉例: 在1kHz 的 2次諧波數值取決於2kHz的基頻音壓值; 3次諧波數值取決於3kHz的基頻音壓值..
在頻響完全平直的假設情況下, 這並不會改變結果.
但在一般非平直的情況, 此作法("Use harmonic freg as ref")可將喇叭基頻響應的影響除去.
As an example, suppose the loudspeaker response was flat apart from a 6 dB peak at 2 kHz. 2 kHz is the 2nd harmonic of 1 kHz, so the 2nd harmonic level shown at 1 kHz will be increased by 6 dB due to the boost in the fundamental when using the excitation frequency as the reference. Similarly the 3rd harmonic level at 667 Hz (2/3 kHz) will be boosted by 6 dB.
舉例說明:
假設頻響完全平直, 只在 2kHz有 6dB 的峰值:
(2kHz乃1kHz的2次諧波, 此時在以計算回推激發出的頻率為參考時) 1kHz的2次諧波值將會誤增加 6dB.
另外在667Hz (其3次諧波為2kHz)的3次諧波值也會誤增加 6dB.
If the harmonic frequency were used as the reference the distortion figures would not show this boost. Using the harmonic frequency as the reference also provides a more meaningful view of distortion at frequencies below the LF roll-off of the system as otherwise the distortion levels are boosted as the level of the fundamental drops.
在勾選"Use harmonic freq as ref" 的情況, 則此種誤增的失真值並不會出現, 而且對低頻衰減的頻段以下提供一個更具意義的觀察 (避免因為基頻的低數值造成的誤增量).
Note that this option will not affect the traces when the plot is not normalised, but will still affect the values in the legend if the distortion figures are set to read in percent or in dB relative to the fundamental.
要注意此 "Use harmonic freq as ref" 選項在 "lot normalised to fundamental" 未勾選時,並不會對顯示曲線造成影響.
但若 "Distortion Figures" 是設定為相對於基頻的百分比或音壓值, 則仍會影響圖示的數值.
The Distortion Figures control selects the units that are used for the harmonic distortion levels displayed on the graph legend. The choices are dB SPL, which shows the actual sound pressure level of each harmonic; dB Relative, which shows how many dB the harmonic is below the fundamental; and Percent, which shows the harmonic level as a percentage of the fundamental. The frequency at which the fundamental level is taken depends on the setting of Use harmonic frequency as ref (see above). When the plot is normalised and distortion figures are in percent the Y axis changes to show percent values.
"Distortion Figures" 控制項可選擇圖中顯示方式, 例如dB, SPL等; dB relative則是顯示諧波比其基頻低多少. 或以百分比顯示等.
前面提過, 某基頻音壓參考的頻率與"Use harmonic freq as ref"的設定有關. 當您勾選 "lot normalised to fundamental"且以百分比顯示, 百分比將顯示於Y軸.
The Highest Harmonic control allows the higher harmonics to be hidden if they are not of interest. For example, if Highest Harmonic were set to 3 only the second and third harmonic traces would appear on the graph and in the graph legend.
"Highest Harmonic" 控制項提供可忽略更高次諧波的顯示功能.
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補述來源: https://www.roomeqwizard.com/hel ... aph_distortion.html
Distortion Examples - speaker measurements
Speaker measurements, particularly those made in-room rather than with the benefit of an anechoic chamber, present additional challenges for interpretation.
嘗試解讀室內的喇叭測量, 有著比無響室更加大的挑戰.
Distortion results for electronic components are typically shown as percentages, values relative to the fundamental. Plotting these percentages for speaker measurements can make the results challenging to interpret due to the often highly irregular frequency response of the speaker.
電聲器材的失真度常以相對於基頻百分比的方式顯示, 由於喇叭的頻響的不規則特性, 使得以百分比方式解讀增添難度.
Using the harmonic frequency as reference (see distortion controls above) helps somewhat, but is by no means a complete solution.
My personal preference is to view the distortion results without normalisation, which helps make the effect of the response irregularities apparent and also emphasises the acoustic level of the distortion components, which can be helpful in deciding where they are likely to be audible and where not.
利用REW 失真度測量" Use harmonic freq as ref "控制項多少有幫助, 但絕非完美的解決方案.
作者個人喜好的觀察方式是不勾選"標準化"("lot normalised to fundamental" unchecked), 如此多少對失真的各頻段可聽聞度分析略有助益. |
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發表於 2021-5-9 23:37:39