Recording in Sound Forge 9 with the automatic threshold method
by Gary Rebholz
Most of us know that we can easily record audio into Sound Forge 9 software. Sometimes—maybe most of the time—you just want to start a recording when you're ready to start and end it when you're ready to end. But sometimes that just won't work. You might not always be at your computer when you want recording to start and end. In those cases, Sound Forge software gives you a few automatic methods for starting and stopping recording. When I can't be there to babysit my computer, I most often use the automatic: threshold method to do the babysitting for me. In this article I'll talk about how the threshold method works so that you can use it when you need to be somewhere other than at your computer at the same time that you need to record something.
If you know exactly what time you want to start and stop recording, the Automatic: Time method works perfectly, but many times I don't know exactly when the audio I want to record will begin or end. In such cases, I always reach for Automatic: Threshold recording.
With the threshold method, you set a certain audio level above which Sound Forge software will begin recording. When the application detects an incoming audio signal that rises above that threshold, it begins recording. When the audio signal level drops back below the threshold level (and stays below it for a specified amount of time) Sound Forge software stops recording. Of course, beyond those simple basics, you have many options for setting up the recording exactly as you want and we'll talk about those options in this article.
You'll find a number of situations for which the threshold methods works better than the other Sound Forge recording methods. For example, I often use Sound Forge software to digitize analog records and tapes. Especially with tapes, I don't always know exactly what's on the tape before I start. Is the whole tape full of audio, or is it just 20 minutes worth even though I'm digitizing a 45-minute cassette? With the threshold method I don't need to know.
Another time threshold recording comes in very handy is when I'm acting as my own audio engineer. For example, I might be recording a narration. My microphone is not right next to my computer because the computer equipment makes too much noise that I don't want recorded. Since my microphone's not in the same place as the computer, I use the threshold method to start and stop recording so I don't have to wear the carpet out walking back and forth between my computer and the vocal booth to start and stop recording.
These are just a couple of examples of when I use threshold recording and many more certainly exist. When you know how to use the method, you'll find your own situations in which it works best. So, let's learn how to use the method effectively.
To get started, assuming you've already connected an audio source to your computer sound card, click the Record button. In the Record dialog, shown in Figure 1, select Automatic: Threshold from the Method drop-down list. Often when I'm using the threshold method I like to set Sound Forge software into Multiple takes creating Regions mode. As you'll see a bit later, you can set Sound Forge software to start and stop recording several times. In Multiple takes creating Regions mode each time recording starts again, the new material will be added to the same file as the previous recording and the two will be identified by region markers which make it very easy to see where your recording stopped and started again.
Choose the channel or channels into which you want to record from the Channels drop-down list. Assuming that the record dialog opened in its default state and that you're recording a stereo audio source (in fact, I'll proceed as if we're recording the outputs of a cassette tape deck), set this to Both.
We'll skip the transport buttons for a moment and take a look at the bottom section of the dialog box. The Meters tab lets you route and monitor the incoming audio source. Click the 1 and 2 icons to see your current routing as shown in Figure 2.
In this figure you can see that I've routed channel one to the left input of the input numbers 7 and 8 pair on my sound card. I'll route channel 2 to the right input of the same pair.
Once you've established your routing, you begin to see activity in the input meters as you raise the volume of the input audio source. Try to find the loudest portion of the tape you're digitizing and set the input level so that it peaks somewhere between -6 and -3 dB during that section. Now, stop the tape playback.
Next, click the Threshold Options tab. On this tab, shown in Figure 3, you set the parameters that control when recording starts and stops.
First, set a Threshold level. This level represents that point at which—when the incoming audio signal rises above it—recording starts. You might need to do some experimenting with this to find the right setting. If you set the level too low (that is, close to the -Inf end of the spectrum), Sound Forge software may start recording before you really want it to. However, if you set this level too high (the 0 dB end), recording may not start when you want it to and you could miss some of the material you wanted to record. This could particularly be a problem if the material you want to record starts out quietly, like a symphony with a quiet introduction, for instance.
Next, set the Release setting. This level represents the length of time the incoming audio signal must remain below the Threshold level (after recording has begun) before Sound Forge software automatically stops recording. Again, you'll have to experiment to find the right length of time being careful not to make it too short so as to end recording before you really want to. For instance, in our example of digitizing a cassette tape, there might be more than five seconds of silence between two songs on the cassette. If you have your release setting at its default of five seconds, Sound Forge software will stop recording before the next song starts. Give yourself plenty of time here so that you're not disappointed later.
Select the Automatically rearm after record checkbox. In a moment you'll arm Sound Forge software for recording. With Sound Forge software armed, the application will respond to the Threshold setting. Without the Automatically rearm after record checkbox selected, if the audio signal falls below the threshold for more than the Release time, Sound Forge software stops recording and never starts again until you manually rearm the application to record. With this checkbox selected, Sound Forge software automatically rearms itself and if the audio signal surpasses the Threshold level again, Sound Forge software begins to record again. This cycle will repeat endlessly until you disarm the application (or you run out of hard-drive space onto which to record).
Now, click the Advanced tab. This tab contains several advanced options, but I'm only interested in one at the moment. Select the Prerecord buffer checkbox. With this option selected, you provide a little bit of protection against the possibility that you set your threshold level too high. Enter a time from 0 to 30 seconds into the Prerecord buffer field—for example, set it to five seconds.
With these settings you've set Sound Forge software up with a record buffer of five seconds. In other words, as soon as you arm Sound Forge software for recording, the application begins recording and constantly keeps five seconds worth of audio in the prerecord buffer.
Let's say then that at exactly 10:00 am the audio signal raises above the threshold and recording begins. When recording ends and you listen back to the recorded material, you find that the material actually starts at 9:59 and 55 seconds. In other words, recording actually started five seconds before the audio signal surpassed the threshold level. This can be a valuable safety net in the event that the material you recorded started out with a few seconds of very low audio level before surpassing the threshold level.
Now that you've got all of your settings as you want them, click the Arm button in the transport bar. A flashing green box to the right of the transport buttons indicates that Sound Forge software is armed and ready to record as shown in Figure 4.
Now, play the cassette. Sound Forge software remains in the armed state until the audio signal surpasses the threshold level at which point recording begins. The flashing green box changes to a solid red box that indicates Sound Forge software is recording.
When you stop the cassette machine, Sound Forge software continues recording until the signal remains below the threshold setting for the duration of the release time. Now, assuming you selected the Automatically rearm after record checkbox, Sound Forge software rearms itself and waits for the signal to rise above the threshold setting again.
When you're done with your session, click the Stop button to disarm Sound Forge software. Click the close button to close the Record dialog and you now have a data window open in the Sound Forge software workspace that contains your recorded material.