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Should you always hear hiss before the music starts?

When you put your ear to the speaker, then there's always a little bit of hiss before the music starts. "Should it be like this?" says an RP visitor.

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A question from a Audio Masterclass visitor...

Hello, my name is Cyrus and I have been sound engineering for about three years. I noticed when I turn a MIDI track into real audio (drum track for example) I think I hear hiss. You can only really hear it if you put your ear up close to the speaker. If you edit the spaces it goes clean. I played some old Led Zeppelin and Jefferson Airplane [the photo is Grace Slick of Jefferson Airplane] and there was hiss when the music started (those are old recordings). Some newer ones had it but less of it. Is there always a little bit of hiss when the music starts if your ear is up to the speaker?

Cyrus

You know, I asked myself that same question, a long long time ago back in my early teenage years (when you could often see small dinosaurs right there in the back yard, scavenging for trilobites).

In my case what was puzzling me was the good old vinyl LP record. When I lowered the stylus onto the record I could hear some noise, but when the music started the noise suddenly got louder. And then in the gaps between tracks the noise became much lower in level again.

My feeling at the time was that it was something to do with the spacing between the grooves, because I could see a correlation - when the grooves were widely spaced at the beginning and between the tracks, then the background noise was low; when the grooves were closely spaced when the music was playing, then the noise was higher.

Of course I now know the real reason - music in those days was originally recorded on analog tape, which created a lot of its own hiss, and you could clearly hear it as a background to the music. And when recordings were prepared for mastering onto vinyl, non-magnetic leader tape was spliced at the beginning, end and in between the tracks.

Hence the only noise before, in between and after the tracks was the intrinsic noise of the vinyl itself. When the music was playing, the noise of the analog tape recording was audible.

What Cyrus is experiencing is the difference between MIDI and recorded audio.

When you record a MIDI track using a sequencer and a MIDI sound module, then when no notes are playing, the sound module produces near-zero background noise. When you play a note, the note itself drowns out any slight noise that might be present. And when the note ends there is silence once more.

But when you convert this to an audio track - I presume you are using MIDI-to-audio conversion software - then the audio recording itself possesses a noise background. So between the notes you hear this noise. And, as you have experienced, there can be a burst of noise before the music starts.

Old Led Zeppelin and Jefferson Starship recordings were made on analog tape, so they too are noisy, and this noise can be audible in digital files made from the recordings.

The good news is that you can achieve lower noise levels.

If you are hearing noise in your MIDI-to-audio conversions, then this is being generated by the software you are using.

If you bought an audio interface for your computer and installed audio recording software, then you could connect the output of your sound module to this.

With correct settings applied, you will find that the noise level is so low that you can hardly hear it. The noise never goes away entirely, but it should be extremely low.

An interesting question, fortunately with a straightforward solution.

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By David Mellor Thursday November 30, 2006
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