Updating instructions to remove libgroove

INSTALL.md

 * [Node.js/NPM](https://nodejs.org/) v0.11.2 or greater
 * [node-canvas dependencies](https://github.com/Automattic/node-canvas#installation)
 * [FFmpeg](https://www.ffmpeg.org/)
-* [libgroove](https://github.com/andrewrk/libgroove)
 
 If you're using a particularly fancy distributed setup you'll also need to install [Redis](http://redis.io/).
 
 An example bootstrap script for installing Audiogram on Ubuntu looks like this:
 
 ```sh
-# 14.04 only: add PPAs for FFmpeg and Libgroove
+# 14.04 only: add PPA for FFmpeg
 # Not required for 15.04+
 sudo add-apt-repository ppa:mc3man/trusty-media --yes
-sudo apt-add-repository ppa:andrewrk/libgroove --yes
 
 # Update/upgrade
 sudo apt-get update --yes && sudo apt-get upgrade --yes
 sudo apt-get install git nodejs npm \
 libcairo2-dev libjpeg8-dev libpango1.0-dev libgif-dev build-essential g++ \
 ffmpeg \
-libgroove-dev zlib1g-dev libpng-dev \
 --yes
 
 # Install Redis if you plan to use it to share rendering among multiple processes/servers
 
 1. [Node.js/NPM](https://nodejs.org/)
 2. [node-canvas dependencies](https://github.com/Automattic/node-canvas#installation)
-4. [libgroove](https://github.com/andrewrk/libgroove)
-
-You probably don't need to install FFmpeg separately because libgroove depends on it.
+4. [FFmpeg](https://www.ffmpeg.org/)
 
 You can install Node.js by [downloading it from the website](https://nodejs.org/).
 
-Installation of node-canvas dependencies and libgroove might look like the following with [Homebrew](http://brew.sh/) (you'll want to make sure [XCode](https://developer.apple.com/xcode/) is installed and up-to-date too):
+Installation of node-canvas dependencies and FFmpeg might look like the following with [Homebrew](http://brew.sh/) (you'll want to make sure [XCode](https://developer.apple.com/xcode/) is installed and up-to-date too):
 
 ```sh
 # Install Git if you haven't already
 brew install git
 
-# Install Cairo, Pango, libgif, libjpeg, libgroove, and FFmpeg
+# Install Cairo, Pango, libgif, libjpeg, libpng, and FFmpeg
 # You may not need to install zlib
-brew install pkg-config cairo pango libpng jpeg giflib libgroove ffmpeg
+brew install pkg-config cairo pango libpng jpeg giflib ffmpeg
 
 # Go to the directory where you want the audiogram directory
 cd /where/to/put/this/
 
 Follow the [Homebrew troubleshooting guide](https://github.com/Homebrew/brew/blob/master/share/doc/homebrew/Troubleshooting.md#troubleshooting), particularly making sure that XCode is up to date.
 
-### Installing libgroove manually
-
-If you're on a Mac and installing [libgroove](https://github.com/andrewrk/libgroove) with Homebrew failed for some reason, you can try following the instructions in the repo to install it more manually.
-
-### Installing XCode command line tools
-
-Audiogram uses [waveform](https://github.com/andrewrk/waveform), which requires the development version of `zlib`. Your Mac might already have this, but if it doesn't, installing XCode command line tools might help:
-
-```sh
-xcode-select --install
-```
-
 ### Updating node-gyp
 
 Updating node-gyp to a current version with:

lib/pcm.js

 var spawn = require("child_process").spawn,
     stream = require("stream");
 
-// Forked from https://github.com/jhurliman/node-pcm
+// Based on https://github.com/jhurliman/node-pcm
+// Modified to respect channels, use fewer vars, and return a stream
 module.exports = function(filename, options) {
   var sampleStream = new stream.Stream(),
       channels = 2,