Why use an audio interface?

An audio interface gives a cleaner signal than a computer microphone. It can eliminate room noise. Musicians and podcasters use them with external instruments and microphones. Also an audio interface may offer a way to send audio to a Raspberry Pi.

Application- tv_commercial_silencer

tv_commercial_silencer monitors live audio, detects and automatically mutes commercials It compares live audio input to a database of “acoustic fingerprints” generated from previously recorded commercials.

recording and monitoring television audio

tv recording system — Television stereo audio line level outputs to Focusrite Scarlett 2i4 audio interface.

Configure macOS to use audio interface input

Go to System Preferences / Sound / Input. Select the interface.

Configuring Raspberry Pi Raspbian to use audio interface input

I’ve seen online reports of people doing this. I haven’t done it yet.

Digital Audio Workstation (DAW)

In Ableton Live Lite I set the input as 1/2 for stereo. Then I recorded audio, split and trimmed into individual clips, one per commercial.

mp3 files

I exported each clip as a mp3 file. mp3 maintains separate stereo channels. In tv_commercial_silencer I stored the files locally in directory data/commercial_mp3. The project .gitignore ignores the data directory and the recordings aren’t commited to the repository.

Appendix- audio interface configuration

input jacks

These accept 1/4 inch (6.35 mm) diameter phone plugs. Can use TR (tip ring, 2 contacts) or TRS (tip ring sleeve, 3 contacts)

unbalanced input

Ok for short cables < 20 foot long. If you connect TR plug, connection is unbalanced mono.

balanced input

Good noise rejection over long cable runs. Uses 1/4 inch phono plug TRS (tip ring sleeve 3 contacts) One wire carries -1 * signal in another wire, third wire is ground. If you connect a TRS plug, the interface attempts to process it as a mono “balanced” audio connection.

how to connect line level stereo input

NOTE: 3 wire stereo output from television must be split out to 2 mono TR plugs, then each plugged in to channel 1 and 2. I put TIP (gray) on channel 1 and RING (red) on channel 2.

input gain knob

Turn up as long as ring light is green. If ring light turns red, amp is clipping. Reduce gain. I set both channel 1 and channel 2 to approximately 1 o’clock position.