add Helm, a polyphonic synthesizer, standalone or lv2

pkgs/applications/audio/helm/default.nix

@@ -0,0 +1,50 @@
+{ stdenv, fetchgit, xorg, freetype, alsaLib, libjack2
+, lv2, pkgconfig, mesa }:
+
+stdenv.mkDerivation rec {
+  name = "helm-git-2015-09-11";
+
+  src = fetchgit {
+    url = "https://github.com/mtytel/helm.git";
+    rev = "ad798d4a0a2e7db52e1a7451176ff198a393cdb4";
+    sha256 = "0ic4xjikq7s2p53507ykv89844j6sqcd9mh3y59a6wnslr5wq1cw";
+  };
+
+  buildInputs = [
+    xorg.libX11 xorg.libXcomposite xorg.libXcursor xorg.libXext
+    xorg.libXinerama xorg.libXrender xorg.libXrandr
+    freetype alsaLib libjack2 pkgconfig mesa lv2
+  ];
+
+  installPhase = ''
+    mkdir -p $out/bin
+    mkdir -p $out/lib/lv2
+    cp -a standalone/builds/linux/build/* $out/bin
+    cp -a builds/linux/LV2/* $out/lib/lv2/
+  '';
+
+  meta = with stdenv.lib; {
+    homepage = http://tytel.org/helm;
+    description = "A free, cross-platform, polyphonic synthesizer";
+    longDescription = ''
+      A free, cross-platform, polyphonic synthesizer.
+      Features:
+        32 voice polyphony
+        Interactive visual interface
+        Powerful modulation system with live visual feedback
+        Dual oscillators with cross modulation and up to 15 oscillators each
+        Unison and Harmony mode for oscillators
+        Oscillator feedback and saturation for waveshaping
+        12 different waveforms
+        7 filter types with keytracking
+        2 monophonic and 1 polyphonic LFO
+        Step sequencer
+        Lots of modulation sources including polyphonic aftertouch
+        Simple arpeggiator
+        Effects: Formant filter, stutter, delay
+    '';
+    license = stdenv.lib.licenses.gpl3;
+    maintainers = [ maintainers.magnetophon ];
+    platforms = platforms.linux;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -15077,6 +15077,8 @@ let
 
   hatari = callPackage ../misc/emulators/hatari { };
 
+  helm = callPackage ../applications/audio/helm { };
+
   hplip = callPackage ../misc/drivers/hplip { };
 
   hplipWithPlugin = hplip.override { withPlugin = true; };