Monday, October 04, 2010

Are you using "silence sense?" Are you using it properly?

This is written to help you do just that. (apologies, if I RANT a bit along the way)


The purpose of an automation silence sensor is to catch “machine failures.” These days, thanks to the reliability of digital equipment, it more often than not catches more human errors and can compound them.

The silence sense feature on your “sequencer” is set up to catch minimum sound or noise levels and prevent any pregnant pauses that might result by automatically triggering the next event "immediately." (see below for the reason behind the quotation marks)

Easier said than done!


The sensitivity level of your silence sense should be set significantly above the noise floor of the equipment in use (this can be critical if any limiters precede it). Too high of a threshold setting will result in "nuisance trips" from soft passages in songs, low recording levels etc.

Too low of a threshold setting will result in the silence sense not catching equipment failures due to noise being detected as audio. The usual practice is to select the noisiest audio source (excluding unsquelched receivers and glitching digital CD or hard drive players - failures in these sources must be detected by other means), set the threshold to just barely detect this noise level, then turn the threshold up 6 db or so.

The silence sense should not step the automation immediately upon sensing silence, because short pauses in the audio occur frequently without machine malfunction. The silence sense delay should be set long enough to avoid nuisance trips, yet short enough to limit the amount of dead air which will be tolerated in the event of a machine malfunction. There is no standard setting here that always works - it is dependent on format, equipment reliability and market competitiveness. The delay must be set longer than normally occurring pauses in the programming. A setting of somewhere between two seconds and five seconds is common. Classical and some Oldies formats may require longer. Shorter settings will result in nuisance trips in almost any format.


Back in the pre-consolidation era when dinosaurs still roamed the earth (early 1990’s) when I was GM at Broadcast Programming (now a part of Dial Global), programmer Kelly Hart received a call from a client GM who said he needed his silence sense to be adjusted VERY tight, since his production staff was very sloppy in placing "cue" tones on commercial carts.

That is what originally inspired today’s post. The memo Hart wrote at the time has been sitting in my files since then and I just heard a client station in a syndicated daypart, playing three things on top of one another, making the very same mistake, which reminded me of it.

Silence sense simply is not a backup to EOM tones, particularly on “cart walled” audio, and it simply can't be used in this way without causing problems.. Setting the delay short enough to keep stop sets flowing will no doubt result in nuisance trips.

A better solution would be to train operators to properly place the tones on the message and maintain the entire system so that the tones work.


And, in spite of all attempts to "do it right," there are occasional songs that a produced containing pauses that are longer than anyone would have expected when setting up a station silence sensor.

For example, with those AC formats still playing Whitney Houston's "I Will Always Love You", the threshold must be set at least 15db below the operating level (-15 VU), and the delay must be set for at least 2.9 seconds. 

Higher thresholds or shorter delays will result in the song tripping the silence sense (more than once!) during the intro, stepping the automation into the next event before the song really even gets started.

Here is the actual step by step process that the Whitney Houston song "I Will Always Love You" puts your automation through so you can better understand what happens.

What follows is the song passage, the length of time of the "low" that could trip your silence sense.

If I

1.67 Sec

Should Stay

2.9 Sec

I would only be in your way

1.4 Sec

So I'll go

.77 Sec

But I know

1.73 Sec

I'll think of you every step of

1.33 Sec

The way

1.87 Sec

Total of 5.87 Sec if silence sense set for -15db.

If in the above case your silence sense simply cannot be changed, the only solutions are to A) not play Whitney Houston, B) edit out a portion of the longest silent stretch, or C) re-record the song with a subaudible tone mixed in during the intro.

What other songs in your library do the same thing? Why don't we simply place subaudible tones behind all such songs when we record the digital master?

At least three reasons I can think of:

1. Subaudible tones can cause problems with older analog automation players, still in use at more stations than you’d think. 

2. PPM’s encoder lives in subaudible tone spaces too (and may also be audibile in those long silences if you try to cover them with a different tone). PPM encoding is programmed NOT to play during any silences.

3. The tone must be low enough (in frequency) to not false trip the 25 Hz EOM detector, yet high enough to pass through the recording and playback equipment without distortion. Many older devices will distort subaudible tones, and the distortion products then become audible.

As a result, my advice is to place the best quality audio, direct from a digital source whenever possible, onto the hard drive/player.

Your goal is, of course, to give listeners as high quality as possible: a faithful, exact copy of the original hit (yes, I know... they probably listen to it today as an mp3, but don’t get me started on THAT!).

After all, you are also going to crunch it, EQ it, compress it, expand it, if you’re like me, using aggressive audio processing so that you’re the biggest, loudest thing on the dial locally (which is more equipment that wants to mess with those pauses of Whitney’s, of course, but, that’s at least one other blog post for another day!).

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