Input monitoring

Being able to hear plug-in audio effects applied to a live signal is an exciting feature of SONAR. However, there are two issues that users commonly stumble upon when using the input monitoring feature. The first is that the monitored signal seems to have an echo associated with it. The second is that live input monitoring can lead to nasty feedback problems, particularly if you have an outboard audio mixer, or you record from a different sound card from the one you are playing back with.

SONAR has several buttons to control input monitoring:

Per-track Input Echo button. Each audio track has an Input Echo button that turns that track’s input monitoring on or off.

Global Input Echo button. The Input Echo On/Off All Tracks button in the Control Bar’s Mix module turns input monitoring on or off on all audio tracks with one click.

Audio Engine button. To disable all audio activity in SONAR, including input monitoring, click the Audio Engine on/off button in the Control Bar’s Mix module so it dims.

 

Note: When you use input monitoring, make sure that the track you’re playing through uses the same audio interface (sound card) for both input and output. Using different audio interfaces for a track’s input and output can produce distortion during input monitoring.

To understand the echo and feedback problems, let’s look at how audio signals travel through your sound card, the drivers, and SONAR. The following diagram depicts a simplified version of this signal flow.

The bottom block of the picture represents the sound card. The shaded area above it represents the audio drivers. The unshaded area at the top represents the main environment of the operating system.

As the diagram shows, analog audio flows into the card's line input (on the left), and is immediately split in two. One branch goes up through the analog-to-digital converter (ADC), where the audio is digitized, buffered and fed to the driver (labeled Wave In in the diagram).

The digital audio data buffers are read by SONAR from the Wave In driver, processed, and then sent out to the Wave Out driver. The driver passes the digital audio buffers through a digital-to-analog converter (DAC), where the audio data is converted back to an analog signal.

Finally, this analog output signal is mixed with the original branch of the input analog signal, and the summed result is presented to the sound card's line output.

With this information in hand, let's follow a simple audio signal through the system to understand how echoes get introduced into the input monitor path.

Suppose you are counting “1, 2, 3" into your sound card very quickly. When you say the first “1,” this sound immediately appears in all the places indicated in the illustration above. In other words, the analog audio signal is pure electrical signal traveling at the speed of light, so it is immediately present across all analog audio paths inside the sound card.

Next, you say “2.” In the time it takes you do that, the ADC has converted the “1” to digital form and the Wave In driver has fed it to SONAR for processing. SONAR processes the buffer right away and passes the processed data right back to the Wave Out driver.

Finally, you say “3.” By this time the original “1” has been converted back to analog audio by the DAC, and that analog signal is mixed in with the “3” you have just said. The ultimate result is that you hear a “1” and “3” mixed together at the line output of card—seemingly sounding like an echo, but actually just an artifact of the signal flow through the system.

You can eliminate the echo by muting the line-in from playing back (see To eliminate the echo from input monitoring); you’ll send only the processed signal to the sound card outputs. This technique introduces a little extra latency to what you hear coming out of your sound card, but if you use WDM or ASIO drivers with your sound cards, the latency is negligible.

The feedback problem results whenever you have a loop in your mixer path: the output of your mixer is patched into the input of your sound card. Feedback can happen with or without input monitoring, but since input monitoring can add several levels of gain to the signal flow, it’s of greater concern when you have input monitoring enabled. Input monitoring is disabled by default when you install SONAR, and you enable it with the following procedure.

To enable input monitoring

Turn your speakers down, and on an audio track that you want to monitor, click the Input Echo button so that it’s lit up (on) . To disable monitoring for this track, click the button off.

Or

Turn your speakers down, then click the Input Echo On/Off All Tracks button in the Control Bar’s Mix module. This enables input monitoring on all tracks. To disable monitoring for all tracks, click the button again.

Now you can hear your instrument in real time with any plug-in effects that you want to patch into the current track. You might also hear an echo, because the dry signal is coming out of your sound card slightly ahead of the processed signal. To eliminate the dry signal, see the next procedure.

To eliminate the echo from input monitoring

1.	Open the Windows Volume Control window:

Windows 7: Click the Windows Start button and go to Control Panel > Hardware and Sound > Volume Control.

The Volume Control window appears.

2.	In the Play Control window of the mixer, select the Mute check box in the Line-In column, or in the column of whatever jack your instrument is plugged into, and close the mixer window.

Now you can hear only the processed sound when you use input monitoring. Using WDM or ASIO drivers for your sound card keeps latency to a negligible amount.

Note: This procedure does not eliminate feedback from your system, only the echo. If you experience feedback, you have a feedback loop somewhere in your mixer setup.

To enable input monitoring when arming tracks

 

Warning: Be extremely careful when enabling input monitoring on an armed track if you are working in a room that contains both live microphones and studio monitors. In such a scenario, enabling input monitoring on an armed track can result in an extremely loud feedback loop between the microphones and monitors and can damage your ears and speakers.

SONAR makes it possible to automatically enable input monitoring when arming a track for recording. To do so, hold down the SHIFT key while you click on a track’s Arm button . Likewise, holding down the SHIFT key while disabling record during playback will disable input monitoring.

To automatically disable input monitoring during playback

Go to Edit > Preferences > Audio - Playback and Recording and clear the Disable Input Monitoring during Playback check box.

When this option is enabled, input monitoring will be disabled on all tracks during playback but not during recording.

 

See also:

Live Input PDC override

Arming tracks for recording