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Lec 2 Changes
author Michael T iMac <Michael.Terrell@eecs.qmul.ac.uk>
date Mon, 30 Sep 2013 10:25:09 +0100
parents 5a9b7fc25eec
children dfd61fe556d5 5a63aa0913ef
files Lectures/Lec2 - Microphones/Lec2 - Microphones.aux Lectures/Lec2 - Microphones/Lec2 - Microphones.log Lectures/Lec2 - Microphones/Lec2 - Microphones.nav Lectures/Lec2 - Microphones/Lec2 - Microphones.pdf Lectures/Lec2 - Microphones/Lec2 - Microphones.synctex.gz Lectures/Lec2 - Microphones/Lec2 - Microphones.tex
diffstat 6 files changed, 192 insertions(+), 175 deletions(-) [+]
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--- a/Lectures/Lec2 - Microphones/Lec2 - Microphones.aux	Thu Sep 19 10:44:17 2013 +0100
+++ b/Lectures/Lec2 - Microphones/Lec2 - Microphones.aux	Mon Sep 30 10:25:09 2013 +0100
@@ -154,8 +154,10 @@
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 \@writefile{nav}{\headcommand {\slideentry {1}{1}{64}{64/64}{ Microphones}{0}}}
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-\@writefile{nav}{\headcommand {\beamer@documentpages {64}}}
-\@writefile{nav}{\headcommand {\def \inserttotalframenumber {64}}}
+\@writefile{nav}{\headcommand {\slideentry {1}{1}{65}{65/65}{ Microphones}{0}}}
+\@writefile{nav}{\headcommand {\beamer@framepages {65}{65}}}
+\@writefile{nav}{\headcommand {\beamer@partpages {1}{65}}}
+\@writefile{nav}{\headcommand {\beamer@subsectionpages {1}{65}}}
+\@writefile{nav}{\headcommand {\beamer@sectionpages {1}{65}}}
+\@writefile{nav}{\headcommand {\beamer@documentpages {65}}}
+\@writefile{nav}{\headcommand {\def \inserttotalframenumber {65}}}
--- a/Lectures/Lec2 - Microphones/Lec2 - Microphones.log	Thu Sep 19 10:44:17 2013 +0100
+++ b/Lectures/Lec2 - Microphones/Lec2 - Microphones.log	Mon Sep 30 10:25:09 2013 +0100
@@ -1,4 +1,4 @@
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--- a/Lectures/Lec2 - Microphones/Lec2 - Microphones.nav	Thu Sep 19 10:44:17 2013 +0100
+++ b/Lectures/Lec2 - Microphones/Lec2 - Microphones.nav	Mon Sep 30 10:25:09 2013 +0100
@@ -131,8 +131,10 @@
 \headcommand {\beamer@framepages {63}{63}}
 \headcommand {\slideentry {1}{1}{64}{64/64}{ Microphones}{0}}
 \headcommand {\beamer@framepages {64}{64}}
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-\headcommand {\beamer@subsectionpages {1}{64}}
-\headcommand {\beamer@sectionpages {1}{64}}
-\headcommand {\beamer@documentpages {64}}
-\headcommand {\def \inserttotalframenumber {64}}
+\headcommand {\slideentry {1}{1}{65}{65/65}{ Microphones}{0}}
+\headcommand {\beamer@framepages {65}{65}}
+\headcommand {\beamer@partpages {1}{65}}
+\headcommand {\beamer@subsectionpages {1}{65}}
+\headcommand {\beamer@sectionpages {1}{65}}
+\headcommand {\beamer@documentpages {65}}
+\headcommand {\def \inserttotalframenumber {65}}
Binary file Lectures/Lec2 - Microphones/Lec2 - Microphones.pdf has changed
Binary file Lectures/Lec2 - Microphones/Lec2 - Microphones.synctex.gz has changed
--- a/Lectures/Lec2 - Microphones/Lec2 - Microphones.tex	Thu Sep 19 10:44:17 2013 +0100
+++ b/Lectures/Lec2 - Microphones/Lec2 - Microphones.tex	Mon Sep 30 10:25:09 2013 +0100
@@ -388,10 +388,45 @@
 	\end{columns}
 \end{frame}
 
+\separator{Microphone Comb Filtering}
+
+\begin{frame}
+	\frametitle{Multiple Microphone Comb Filtering}
+	\begin{itemize}
+		\item Multiple microphones recording a common source will be susceptible to comb filtering.
+	\end{itemize}
+	\begin{figure}
+		\includegraphics[width = 0.8 \textwidth]{Figures/guitarMicPic.pdf}
+	\end{figure}
+\end{frame}
+
+
+\begin{frame}
+	\frametitle{Multiple Microphone Comb Filtering}
+	\begin{figure}
+		\includegraphics[width = 0.8 \textwidth]{Figures/micImpulse.pdf}
+	\end{figure}
+	\begin{figure}
+		\includegraphics[width = 0.8 \textwidth]{Figures/combFilter.pdf}
+	\end{figure}
+\end{frame}
+
+
+\begin{frame}
+	\frametitle{Time Offset Correction}
+	\begin{itemize}
+		\item A time delay, $\tau$, is added to the close mic to align the signal with the far mic.
+	\end{itemize}
+	\begin{figure}
+		\includegraphics[width = 0.8 \textwidth]{Figures/micImpulseAligned.pdf}
+	\end{figure}
+\end{frame}
+
+
 \separator{Spatial Microphone Techniques}
 
 \begin{frame}
-	\frametitle{Spatial microphone techniques}
+	\frametitle{Spatial Microphone Techniques}
 	\begin{itemize}\itemsep12pt
 		\item When we listen to live music a sense of the space and source position in which we are listening is encoded into what we hear.
 		\item A range of microphone techniques are used to capture a sense of this spaciousness.
@@ -409,6 +444,37 @@
 \end{frame}
 
 \begin{frame}
+	\frametitle{Spaced Omnis}
+	\begin{center}
+	\includegraphics[width=3.5in]{Figures/Omnis.eps}\\ 
+	\vspace{0.4cm}
+	$\frac{x}{3}\leq y \leq \frac{x}{2}$
+	\end{center}
+\end{frame}
+
+\begin{frame}
+	\frametitle{Spaced Omnis}
+	\begin{itemize}\itemsep12pt
+		\item Phase difference may change with frequency giving an unclear image $\rightarrow$ can be an advantage, e.g. for piano, choir, organ.
+		\item Subject to the ``hole in the middle'' effect if distance between the mics is large, whereby the time of arrival and level difference makes the image seem wider.
+		\item Decca tree attempts to solve this by adding a central mic slightly in front of the pair. (Decca also require a pair of wider mics, giving a total of 5 omnis.)
+	\end{itemize}
+\end{frame}
+
+\begin{frame}
+	\frametitle{Coincident Stereo Mic Techniques}
+	\begin{itemize}\itemsep14pt
+		\item Coincident stereo techniques place the two microphones at the same point in space to eliminate comb filter effects.
+		\item The image width is controlled by:
+		\begin{itemize}\itemsep6pt\vspace{.2cm}
+			\item The type of microphone capsules.
+			\item The angle between the microphones.
+			\item The distance from the microphones to the sources.
+		\end{itemize}
+	\end{itemize}
+\end{frame}
+
+\begin{frame}
 	\frametitle{Blumlein Coincident Figure-of-Eights at 90$^{\circ}$}
 	\begin{center}
 	\includegraphics[width=3in]{Figures/Blumlein.eps}
@@ -417,12 +483,11 @@
 
 \begin{frame}
 	\frametitle{Blumlein Coincident Figure-of-Eights at 90$^{\circ}$}
-	\begin{itemize}
-		\item Fully left is at dead axis of right mic.
-		\item Only front 90$^{\circ}$ are usable for direct sound due to out of phase regions.
-		\item Very accurate mapping of physical position to image within front 90$^{\circ}$.
-		\item Out of phase and left-right reversed regions no problem for reverberation since it is random and incoherent anyway.
-		\item Can take sum and difference to get Mid and Side signals instead - can control stereo width with 1 fader.
+	\begin{itemize}\itemsep8pt
+		\item Fully left is on the dead axis of the right mic (and vice versa).
+		\item Only the front 90$^{\circ}$ are usable for direct sound as the other regions are out of phase.
+		\item Very accurate mapping of source position to stereo image within the front 90$^{\circ}$.
+		\item The out of phase (rear) and left-right reversed regions aren't a problem for reverberation since it is random and incoherent.
 	\end{itemize}
 \end{frame}
 
@@ -435,11 +500,11 @@
 
 \begin{frame}
 	\frametitle{Back-to-Back Cardioids}
-	\begin{itemize}
-		\item No out of phase regions.
-		\item Frequency response at front is poor especially with large diaphragms.
-		\item Very wide front angle
-		\item Can narrow the angle between capsules down to 90$^{\circ}$ to give a better response at the front, as well as a narrower stereo image. Optimum angle is about 130$^{\circ}$.
+	\begin{itemize}\itemsep8pt
+		\item There are no out of phase regions.
+		\item The frequency response at front is poor, because the off-axis response of a cardioid will vary with frequency.
+		\item The very wide front angle enables wide sources to be captured.
+		\item The angle between capsules can be reduced down to 90$^{\circ}$ to give a better response at the front, as well as a narrower stereo image. The optimum angle is about 130$^{\circ}$.
 	\end{itemize}
 \end{frame}
 
@@ -475,11 +540,11 @@
 	\end{center}
 	
 	\column{1in} \begin{center}
-	Cardioids\\
+	Figure of Eights\\
 	$\downarrow$\\$\downarrow$\\$\downarrow$\\$\downarrow$\\
 	Hypercardioids\\
 	$\downarrow$\\$\downarrow$\\$\downarrow$\\$\downarrow$\\
-	Figure of Eights
+	Cardioids
 	\end{center}
 	
 	
@@ -488,25 +553,6 @@
 \end{frame}
 
 \begin{frame}
-	\frametitle{Spaced Omnis}
-	\begin{center}
-	\includegraphics[width=3.5in]{Figures/Omnis.eps}\\ 
-	\vspace{0.4cm}
-	$\frac{x}{3}\leq y \leq \frac{x}{2}$
-	\end{center}
-\end{frame}
-
-\begin{frame}
-	\frametitle{Spaced Omnis}
-	\begin{itemize}
-		\item Good for smaller sources.
-		\item Phase difference changes with frequency $\therefore$ image is not clear. Can be an advantage for e.g.\ piano, choir, organ.
-		\item Subject to the ``hole in the middle'' effect. If there is a large time of arrival and large level difference the brain makes the image wider.
-		\item Decca tree attempts to solve this by adding a central mic slightly in front of the pair. (Decca also require a pair of wider mics, giving a total of 5 omnis.)
-	\end{itemize}
-\end{frame}
-
-\begin{frame}
 	\frametitle{Near-Coincident Techniques}
 	\begin{center}
 	\includegraphics[width=3.3in]{Figures/nearcoincident.pdf}\\
@@ -516,11 +562,11 @@
 
 \begin{frame}
 	\frametitle{Spot Mics}
-	\begin{itemize}
-		\item Usually mono and panned.
-		\item Can have stereo pair for wide sources e.g.\ woodwind section of an orchestra.
-		\item Must pan to same position as in main pair.
-		\item Image tends to collapse towards spots due to Haas effect, so must use several at different positions.
+	\begin{itemize}\itemsep8pt
+		\item Individual mono mics placed very close to a single source, e.g. snare drum mic on a drum kit.
+		\item Often used in conjunction with stereo recordings, and must be panned to the same position.
+		\item Spot mics may be a stereo pair for a wide source in a large ensemble, e.g. the woodwind section within an orchestra.
+		\item A spot mic recording is unlikely to sound natural due to the close proximity of mic and source.
 	\end{itemize}
 \end{frame}
 
@@ -548,42 +594,6 @@
 	\end{columns}
 \end{frame}
 
-
-
-\separator{Microphone Comb Filtering}
-
-\begin{frame}
-	\frametitle{Multiple Microphone Comb Filtering}
-	\begin{itemize}
-		\item Multiple microphones recording a common source will be susceptible to comb filtering.
-	\end{itemize}
-	\begin{figure}
-		\includegraphics[width = 0.8 \textwidth]{Figures/guitarMicPic.pdf}
-	\end{figure}
-\end{frame}
-
-
-\begin{frame}
-	\frametitle{Multiple Microphone Comb Filtering}
-	\begin{figure}
-		\includegraphics[width = 0.8 \textwidth]{Figures/micImpulse.pdf}
-	\end{figure}
-	\begin{figure}
-		\includegraphics[width = 0.8 \textwidth]{Figures/combFilter.pdf}
-	\end{figure}
-\end{frame}
-
-
-\begin{frame}
-	\frametitle{Time Offset Correction}
-	\begin{itemize}
-		\item A time delay, $\tau$, is added to the close mic to align the signal with the far mic.
-	\end{itemize}
-	\begin{figure}
-		\includegraphics[width = 0.8 \textwidth]{Figures/micImpulseAligned.pdf}
-	\end{figure}
-\end{frame}
-
 \separator{Microphone Placement}
 \large
 \begin{frame}