Affichage des messages dont le libellé est An audiophile fact : north American FM sounds more colourful than elsewhere. Afficher tous les messages
Affichage des messages dont le libellé est An audiophile fact : north American FM sounds more colourful than elsewhere. Afficher tous les messages

An audiophile fact : north American FM sounds more colourful than elsewhere

An audiophile fact : north American FM sounds more colourful, and it is really pleasing!

Any audiophile who visited North America and had a chance to listen to the local FM radio stations must have felt that there's a noticeable difference between North American FM sound quality vs. anywhere else in the world.

What explains that difference is the fact that the pre-emphasis stage (used to lower the noise in the highest frequencies) is different in north America.

Also, that explains why european radio tuners must be adapted when used in the USA… Their 50 µs de-emphasis circuitry must be transformed into 75 µs, otherwise they sound like "thumping".

Of course for the regular modern transistor receiver this process does not worth it : it is cheaper to buy another one in a USA electronic store.

For the vintage vaccum tube receivers owned by audiophiles, e.g. the ones that were made in Germany (Grundig…), going the process of replacing some piece of electronics sometimes may worth it. More info about that issue…

> Fm radio…
> Modulation characteristics
> Pre-emphasis and de-emphasis

Random noise has a 'triangular' spectral distribution in an FM system, with the effect that noise occurs predominantly at the highest frequencies within the baseband.

This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver.

Reducing the high frequencies in the receiver also reduces the high-frequency noise.

These processes of boosting and then reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively.

The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit.

In most of the world a 50 µs time constant is used.

In North America, 75 µs is used.

This applies to both mono and stereo transmissions and to baseband audio (not the subcarriers).

The amount of pre-emphasis that can be applied is limited by the fact that many forms of contemporary music contain more high-frequency energy than the musical styles which prevailed at the birth of FM broadcasting.

They cannot be pre-emphasized as much because it would cause excessive deviation of the FM carrier. (Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis—e.g. dbx in the BTSC TV sound system—or none at all.)

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