Ground Loops


groundloopscenariosIf you’ve worked with a sound system you have probably at one point heard a ground loop, but may not know it for what it is.  It usually manifests itself as a 60Hz buzzing sound.  Sometimes you hear this buzzing in the main speakers or monitors, or it may occur on your recording.  So what is it, and how can you avoid it?

groundloopexplained

A ground loop occurs under the following conditions.

1. Two electronic devices are plugged in to different electrical circuits.
2. The two devices are connected via an audio cable.
3. A difference in electrical potential exists between the two electrical grounds that the devices are plugged in to, which causes current to flow between the two devices through the audio cable.

So what can you do about it?  Probably the simplest solution is to use a “hum eliminator.”  These devices are actually just transformers that physically isolate the input and output.   A transformer is just two coils of wire that are wound closely together so that when a current is passed through one it induces a current to flow through the other wire, even though the two wires are not physically touching each other.  A perfect solution for physically isolating two audio devices that we want to connect together.

Musician’s Friend has a whole bunch of devices under thier Hum Eliminator category.  One thing to be aware of is that transformers have a frequency response characteristic.  Meaning, they can color the sound, or start to roll off (attenuate) higher frequencies.  So, some of the cheaper devices may not give you the best audio fidelity.  I’ve been pretty happy with the Ebtech brand for hum eliminators.

ebtech_hum_e

Recording direct to mp3

Many churches record thier sermon’s to mp3.  Usually they record in one format, on a CD, as a wave file, or some other method, and then encode to mp3, in a two step process.  I’m always looking for ways to streamline and simplify the process, especially when volunteers are involved.  Here is a way that you can record direct to mp3.  Assuming all goes well, as soon as you press the stop button on the recording, your file is ready to be uploaded to your podcast or website.

I’ve been using the multi-track recording program REAPER for a while now and have been really impressed with it for the price, $60 for non-profits.  Two things make it perfect for the task of recording direct to mp3.

1. It can record direct to MP3.  Not all recording software will do this, usually they record to a native file format and then allow you to encode to mp3.  Sometimes the encoding process can be confusing for volunteers, using Reaper to record direct to mp3 eliminates this possibility.

2. It allows you to record the “output” of a channel.  What this means is that you can apply effects to a channel as it is recorded.  Again, most other multi-track recording programs require you to record the track dry and then in mixdown apply effects to the channel.  Another step eliminated as you can apply compression and EQ as the track is being recorded.

So all this sounds like something that would benefit you, here is how I’ve set it up.  All that is required is a Windows PC with some sort of audio I/O interface.  Just be aware that your computer will have different audio I/O then what is shown here.

1. Download and install REAPER from www.cockos.com/reaper

2. Download the Lame MP3 encoder from http://lame.buanzo.com.ar/.  Use the download entitled “For Audacity on Windows”.  Unzip the file and place the lame_enc.dll file in the program folder where you installed Reaper.  Most likely that is C:\Program Files\REAPER\.  The first time you try and create an MP3 it will prompt you for where the MP3 encoder is located.  Point it to this file.

3. Add a new track (Ctrl+T) and adjust the Record Mode settings.  You access the record mode settings by pressing the button at the very bottom, to the right of the track meter.  (Or you can right-click on the meter itself to get the same thing.)  Select “Monitor Input” and select “Record: output (stereo)” as shown below.  Also, where it says Stereo Input with an arrow to the right, select the audio inputs on your computer that you want to use.  Note that I’m recording the stereo input here so that all the audio information that is being sent to the computer gets recorded.  Later in the MP3 recording it will be converted to mono to reduce the file size, but here we want to record the stereo input.

reaper_settings1

4. Add any effects you would like to be applied to the recording.  For voice recordings, in this case of a sermon, I usually use compression to keep the volume level consistent.  You can also add EQ and any other of the variety of effects that are available.  (REAPER will use any VST plug-ins you may have.)  To add an effect to a track, click an open slot above the track and you will be prompted for what type of effect you want to insert.  In the image below you can see where I’ve inserted the Reaper Compressor and Reaper EQ.

reaper_settings2

To accomplish step 3-4 above you can also create a track template to make this easily repeatable.  Right click on the track number and select “Save the selected track as a track template.”  Now, instead of doing step 3-4 as described above you would just go to the track menu and select Insert Track from Template and select the template you just saved.  The track will be added with all of the settings and effects you’ve applied.

5. Set the output recording format to MP3.  You do this through the Project Settings, which you can access through the File menu, or simply by pressing Alt+Enter.  Below you can see the settings that I’ve used.  The important one being of course the “Audio format for new recordings” set to MP3 (lame).  I’ve found that 32kbps works pretty well for a 30-45 minute sermon.  It may sound a bit digitized, but it results in an 8-10MB file which is a pretty reasonable download.

reaper_settings3

That’s it!  You’re set to record.  Just click the record button or press CTRL+R to begin recording.  There is however one setting adjustment that I’ve found useful if not mandatory to change for long recording times.  You need to turn off the waveform generation.  The waveform that is drawn on the screen during recording is stored in RAM.  If you make long recordings, this can use up a lot of RAM and start to slow down your computer, even leading to drop outs in the recording.  To make this adjustment, go to the Options menu and click on Preferences at the very bottom of the menu.  Alternatively you can just press CTRL+P to bring up the preferences dialog.

Go to the Recording page and uncheck the Show Preview of Recordings checkbox.  Also select build peaks manually.  You can see these settings below.

reaper_settings4

That’s it!  Happy recording!

Super, a free program to encode video to and from different formats

super_screen_shot

Working for a church, I love open source (free) software that works really well and makes my life easier.  Super is one of those programs.  If you do any kind of media/video work on a PC, you should become familiar with Super.  It will encode video from one format to another.  While sometimes it can be a bit finicky, especially if your source video is of strange codec origins, usually a bit of trial and error will produce satisfactory results.  If you don’t have Adobe’s flash encoder, Super is a great way to encode flash video.  In fact, I use Super as the last step in generating my tutorials to create the flash file that you view online.

Check it out, Super.

(Just a word of warning, the Super website is a pain, you’ve got to click through several pages to get to the actual download page.)

Widescreen in Power Point

Have you ever been given a ppt file that was created on a 4:3 monitor, but you want to project it on a widescreen projector?  Usually when you project this type of file, there are black bars on the left and right sides of the screens and the content is still 4:3.

Here is how you can make the file widescreen.  Go to File – Page Setup, in the width and height boxes enter 16 for width and 9 for height.  Click ok and now your slides are widescreen.

pptwidescreen

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