DE4128727A1 - Mono, stereo or two-tone switching method in TV receiver - switching to stereo reproduction when specified relation is max. and equal to preset threshold value - Google Patents

Abstract

A device determines a value (A) of a pilot carrier (PT) and another one determines the characteristic value (B) of a stereo-carrier (ST) and/or a characteristic value (C) of a two-tone carrier (ZT). The stereo-reproduction is switched over when the ratio of the pilot carrier value and the stereo carrier value is max. equal to a preset threshold value (E). Pref. the two-tone reproduction is switched over when the ratio of the pilot carrier value to the two-tone carrier value equals to the preset threshold value. The mono-reproduction is switched over when the above mentioned ratios are higher than the preset threshold value. USE/ADVANTAGE - Reproduction mode switching in TV receiver, with improved characteristic even in bad reception conditions, or on interference.

Description

The invention relates to a method for mono, stereo or Two-tone switching in a television with one device device for stereo or two-tone playback according to the upper part handle of claim 1.

An identifier or switch security can be by time Lich long detection of the stereo or two-tone sound reach. But if an interfering signal for a long time occurs, even with a very long detection period Error detection and incorrect switchover.

It is an object of the invention, the identifier or Umschaltsi security of stereo, two-tone or mono broadcasts poor reception or interference disturbed by interference signals improve.

The object is achieved according to the method Claim 1 solved. Advantageous further training of the Erfin manure is described in the claims.

The invention according to claim 1 opens up the possibility of to make a switch, the identifier or order switching criterion is independent of interference signals and is included after a short time a safe switchover can be made can. If a transmission of interference signals is disturbed, then the pilot carrier as well as the stereo carrier or the Two-tone carriers disturbed in the same way. The ratio of Amplitude of the pilot carrier to the amplitude of the stereo carrier is therefore independent of interference or field strength fluctuations conditions during transmission.

Now falls below the ratio of pilot carrier to stereo carrier a predetermined threshold value E, it is automatically switched to stereo playback.  

Below the ratio of pilot carrier to two-tone ger the predetermined threshold value E, so on two-tone How automatically switched.

However, the above conditions exceed the above if threshold value E is correct, the system automatically switches to mono-re switched.

The following are available for the detection of the transmission state Signals available: pilot carrier (A), stereo carrier (B) and / or two-tone carrier (C).

With good signals you get egg after a certain time ne certain number of identifiers. If the signal is bad ter or you are on a channel with interference signals you get a small number of identifiers. Now it will Relationship between pilot carrier and identifier formed. To it makes sense if the individual parameters for the stereo carrier or two-tone carrier a certain threshold (with Hysteresis), since a changeover otherwise makes sense is going on because it can be assumed with great certainty that the audio signal is distorted if the amplitude is too small be given.

Whether the circuit is a stereo or two-tone detection leads or makes such a switch depends on the invention depends on whether the ratio of pilot tone carriers divided by stereo or two-tone carriers agreed threshold value above or below.

The predetermined threshold value E is also a Hysteresis in the case of strongly fluctuating pilots value because there is a strong dependency on the video content.

Under the most unfavorable reception conditions, a more secure one Reception achieved with analog multi-tone transmissions. This  results from the independence of the absolute values of the parameters sounds from the transmission. Safe detection of stereo or Two-tone transmission is for a relatively short transmission times possible.

The invention is based on a tabular and Illustrated embodiment illustrated. In the drawing:

Table 1 System parameters for standard B / G television standard

Fig. 1 amplitude / frequency diagram over the location of the sound carrier to the image carrier,

Fig. 2 amplitude / frequency diagram REO on the position of the second audio carrier to the pilot carrier and Ste / Dual carrier,

Fig. 3 flow chart.

Table 1 shows the known system parameters for the TV sound standard B / G. As is known, the first sound channel or sound carrier is 5.5 Mhz and the second sound channel or sound carrier is 5.74 Mhz under the image carrier, as is also shown in FIG. 1.

The pilot carrier frequency is approximately ± 54.7 kHz from the second Sound carrier removed. The stereo identification frequency is ± 117.5 Hz away from the pilot carrier. If the sound is dual or The two-tone signal is omitted for stereo and the characteristic frequency for dual or two-tone is 274.1 Hz from Pilot carrier removed.

In a television set with a detection circuit the two recordings as well as the pilot and the existing the characteristic frequency detected and their amplitude values A, B or C. determined. It becomes the ratio of the amplitude values of the pilot carrier at a characteristic frequency.  

In Fig. 2, the ratio of pilot carrier A to characteristic frequency B or C z. B. the value 2. In an evaluation circuit (not shown) in the television set, the ratio value is compared with a predetermined threshold value 1.8 . The size of the threshold is variable.

In the present case, stereo or two-tone Playback switched. If the ratio is below 1.8 steps or falls below for a certain time switched to mono. It also switches to mono, if the second sound carrier or the pilot carrier or the nominal frequency another predetermined threshold F, G or H fall below.

Claims (5)

1. Method for mono-stereo or two-tone switching in a television set with a device for determining a value (A) of the pilot carrier (PT) and with a device for determining a characteristic value (B) of a stereo carrier (ST) and / or for determining a Characteristic value (C) of the two-tone carrier (ZT), characterized in that it is switched to stereo playback when the ratio of A: B is less than or equal to a first predetermined threshold value (E). 2. The method according to claim 1, characterized in that is switched to two-tone playback when the Ver ratio of A: C less than or equal to the first predetermined Threshold (E). 3. The method according to claim 1 or 2, characterized net that it switches to mono playback when the ratio of A: B or A: C is greater than the first agreed threshold (E). 4. The method according to any one of claims 1-3, characterized shows that it switches to mono playback, if the value (A) for the pilot carrier before a second falls below a certain value (F). 5. The method according to any one of claims 1-4, characterized ge indicates that switched to mono playback if the characteristic value (B) for the stereo carrier or the characteristic value (C) a third predetermined value (G) or falls below (H).