void UpdateDbLayers ()
{
for (int index = -numDBLines; index <= numDBLines; index++) {
var location = Math.Floor (GetLocationForDbValue (index * defaultGain / numDBLines));
if (index >= -numDBLines && index <= numDBLines) {
dbLines [index + 4].Frame = new CGRect (graphLayer.Frame.X, location, graphLayer.Frame.Width, 1f);
dbLabels [index + 4].Frame = new CGRect (0f, location - bottomMargin - 8, leftMargin - 7f, 16f);
}
}
}