1kHz tone.etc. Why?

Does anyone know why they transmitted these tones prior to programmes starting? (and sometimes instead of music on the testcard!)

IIRC BBC1 used 1KHz, but BBC2 used a lower sounding version.

Comments

  • 1 Khz tone is a anice rioudn number to see taht eth audio is teh right level.
    It might seems strange now but because of the analaiogue technolgy being rather heat senstive and generally aged ..... every circuit needed to be tweaked daily before it coudl be used.

    I imagine that 1 Khz came from the telephony world as it is roughly (in octave terms) halfway in the speech band.

    BBC 2 - there was a long debate about this - it is musical A ( about 440Hz ) .. but the musicians could not say which A they wanted so I think the techies set it to 440Hz.

    So the BBC was transmitting Three frequency standards 200Khz, 1 KHz and 440 Hz..

    The upper frequency tone was usually 10Khz - again easy to measure on a meter.

    and for manual line up tioens at varsious frequencies from 120Hz to whatever the upper limit was (often 7Khz) were used and graphs plotted and equalsiers tweaked.

    With more clever technology there were frequency sweeps - first by motorising the frequency knob on the generator - but then electronics took over and could also do warbles and other multifrequency generation and analysis - the "meter" was very important.

  • 4-Tel4-Tel Posts: 607

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    For some reason, both tones changed from being continous to being broken sometime in the early 1990s.

  • 1 Khz tone is a anice rioudn number to see taht eth audio is teh right level.
    It might seems strange now but because of the analaiogue technolgy being rather heat senstive and generally aged ..... every circuit needed to be tweaked daily before it coudl be used.

    I imagine that 1 Khz came from the telephony world as it is roughly (in octave terms) halfway in the speech band.

    BBC 2 - there was a long debate about this - it is musical A ( about 440Hz ) .. but the musicians could not say which A they wanted so I think the techies set it to 440Hz.

    So the BBC was transmitting Three frequency standards 200Khz, 1 KHz and 440 Hz..

    The upper frequency tone was usually 10Khz - again easy to measure on a meter.

    and for manual line up tioens at varsious frequencies from 120Hz to whatever the upper limit was (often 7Khz) were used and graphs plotted and equalsiers tweaked.

    With more clever technology there were frequency sweeps - first by motorising the frequency knob on the generator - but then electronics took over and could also do warbles and other multifrequency generation and analysis - the "meter" was very important.

    So it sounds very much like the same reasons that THEENGINEER told me about concerning the picture.

  • For some reason, both tones changed from being continous to being broken sometime in the early 1990s.

    I used to love that sound, I thought it was the testcard having a bit of fun!.

  • For some reason, both tones changed from being continous to being broken sometime in the early 1990s.

    It was to do with NICAM stereo- the tones switching between speakers.

  • rob1973rob1973 Posts: 4,236

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    And here is the modern take on it.

  • Are there any examples on any video sites? I've tried on Youtube, but to no avail.

  • The tone is used to adjust audio levels to make sure that they are consistent from source to transmitter. It's also known as reference tone because it is generated at 0dB level and all other sound levels should be referenced to it. In other words, peak level in broadcasting is +8dB so any audio can't be more than 8dB above reference.

    Reference tone is used extensively in VT recording, especially analogue, to line up VT machines. The VU meters on the recorders are set to show -4VU when tone is present and this ensures that audio recorded on tape is at the correct level.

    The intermittant tone that was referred to is stereo tone. The BBC used one silent pip on the left channel and two silent pips on the right, repeating every 4 seconds. The independent companies adopted the EBU system of one pip on the left channel repeating every 3 seconds and continuous tone on the right.

  • The tone is used to adjust audio levels to make sure that they are consistent from source to transmitter. It's also known as reference tone because it is generated at 0dB level and all other sound levels should be referenced to it. In other words, peak level in broadcasting is +8dB so any audio can't be more than 8dB above reference.

    Reference tone is used extensively in VT recording, especially analogue, to line up VT machines. The VU meters on the recorders are set to show -4VU when tone is present and this ensures that audio recorded on tape is at the correct level.

    The intermittant tone that was referred to is stereo tone. The BBC used one silent pip on the left channel and two silent pips on the right, repeating every 4 seconds. The independent companies adopted the EBU system of one pip on the left channel repeating every 3 seconds and continuous tone on the right.

    Of course GLITS is neg 3 on each leg in Stereo but is 0 level when the two legs are combined to mono.

  • When the BBC's radio networks used to close down, each of them would put out tone before coming on air, and each had a different frequency so that engineers could identify the various distribution circuits.

    Radio 3's was 440KHz, the A note, for the benefit of musicians who wanted to use it as a tuning fork!

  • The tone is used to adjust audio levels to make sure that they are consistent from source to transmitter. It's also known as reference tone because it is generated at 0dB level and all other sound levels should be referenced to it. In other words, peak level in broadcasting is +8dB so any audio can't be more than 8dB above reference.

    Reference tone is used extensively in VT recording, especially analogue, to line up VT machines. The VU meters on the recorders are set to show -4VU when tone is present and this ensures that audio recorded on tape is at the correct level.

    The intermittant tone that was referred to is stereo tone. The BBC used one silent pip on the left channel and two silent pips on the right, repeating every 4 seconds. The independent companies adopted the EBU system of one pip on the left channel repeating every 3 seconds and continuous tone on the right.

    Before reading this I thought that stereo tone was used by people with stereo TV's to set it correctly.

  • I was told that the ITV companies had a system called "Duo-Tone". Each company had a unique pair of frequencies allocated, and could be used for identing audio lines.

    This was phased out before I joined, and I was never sure if it was a wind-up. The "old" hands were very cruel to us trainees, funny how it rubs off...

    P.

  • The tone is used to adjust audio levels to make sure that they are consistent from source to transmitter. It's also known as reference tone because it is generated at 0dB level and all other sound levels should be referenced to it. In other words, peak level in broadcasting is +8dB so any audio can't be more than 8dB above reference.

    Not quite true now, in 5.1 transmission systems. And regulated by PPm meter not peaks in the UK, so it could be slightly over while still "legal" within 6PPM.

    5.1 systems for certain broadcasters will allow up to -3dbfs below digital peak, but again this is measured mostly with loudness metering with one eye on the digital peaks.

  • All of the above is true, but doesn't answer the OP's question.

    Tone was radiated as a regular part of the trade test (i.e. test card) transmissions because it was an easy way to test a television set at home or on a work bench for 'sound on vision' - a condition when the audio section of the set interfered with the picture. Tone exhibited itself as a regular series of horizontal bars on the picture and was a foolproof way of checking for this problem. The one minute of silence that preceded it was to check for the opposite problem, 'vision on sound' which showed up as a background buzz during the silent periods.

    That was the reason why tone was transmitted as a part of the trade test schedule; however in the early days of TV it often replaced music because when trade had to originate from the transmitting station itself, few in the early days were equipped with the means of playing music, and it was much easier to use an electronically-generated tone which required no manual supervision or intervention. (From the mid 50s, all ITA but not BBC transmitters had turntables and test card music originated at each main station rather than at studios, by the way).

    Tone would also appear shortly before the start of programmes - this came from the studios and was part of the line-up of the circuit from studio to transmitter.

    This is a very simplified answer but should hopefully satisfy the OP!

  • Is it wrong of me to find this stuff fascinating? :o

  • All of the above is true, but doesn't answer the OP's question.

    Tone was radiated as a regular part of the trade test (i.e. test card) transmissions because it was an easy way to test a television set at home or on a work bench for 'sound on vision' - a condition when the audio section of the set interfered with the picture. Tone exhibited itself as a regular series of horizontal bars on the picture and was a foolproof way of checking for this problem. The one minute of silence that preceded it was to check for the opposite problem, 'vision on sound' which showed up as a background buzz during the silent periods.

    That was the reason why tone was transmitted as a part of the trade test schedule; however in the early days of TV it often replaced music because when trade had to originate from the transmitting station itself, few in the early days were equipped with the means of playing music, and it was much easier to use an electronically-generated tone which required no manual supervision or intervention. (From the mid 50s, all ITA but not BBC transmitters had turntables and test card music originated at each main station rather than at studios, by the way).

    Tone would also appear shortly before the start of programmes - this came from the studios and was part of the line-up of the circuit from studio to transmitter.

    This is a very simplified answer but should hopefully satisfy the OP!

    Blimey, sound-on-picture - that's going back to steam driven television alright.

    I always thought that tone was transmitted on trade tests because the TX engineers were using modulation monitors to calibrate the transmitters.

  • All of the above is true, but doesn't answer the OP's question.

    Tone was radiated as a regular part of the trade test (i.e. test card) transmissions because it was an easy way to test a television set at home or on a work bench for 'sound on vision' - a condition when the audio section of the set interfered with the picture. Tone exhibited itself as a regular series of horizontal bars on the picture and was a foolproof way of checking for this problem. The one minute of silence that preceded it was to check for the opposite problem, 'vision on sound' which showed up as a background buzz during the silent periods.

    That was the reason why tone was transmitted as a part of the trade test schedule; however in the early days of TV it often replaced music because when trade had to originate from the transmitting station itself, few in the early days were equipped with the means of playing music, and it was much easier to use an electronically-generated tone which required no manual supervision or intervention. (From the mid 50s, all ITA but not BBC transmitters had turntables and test card music originated at each main station rather than at studios, by the way).

    Tone would also appear shortly before the start of programmes - this came from the studios and was part of the line-up of the circuit from studio to transmitter.

    This is a very simplified answer but should hopefully satisfy the OP!

    It does thanks :) Do you know if the periods of tone instead of music was scheduled or random?

  • It was scheduled

    There's a whole web site:
    http://www.testcardcircle.org.uk/ARTICLES.HTML
    devoted to test cards, trade test colour films, music and tone

    From that site:

    Note the two occasions at 10.25 and 15.25 when tone and one minute's silence was used to immediately precede the showing of a film. Tone was also radiated at:
    09.00 to 0904, 09.30 to 09.34, 10.05 to 10.09, 12.01/30 to 12.04,

    14.20 to 14.24, 16.00 to 16.04, 16.20 to 16.24, 17.00 to 17.04,

    17.20 to 17.24, 18.00 to 18.04, 18.20 to 18.24, 19.01 to 19.04

  • Before the days of 24 hour programming, I seem to remember that radio stations used to broadcast a tone.

    What was this for, as, obviously, it can't be to test the "noise on picture" scenario.

  • Before the days of 24 hour programming, I seem to remember that radio stations used to broadcast a tone.

    What was this for, as, obviously, it can't be to test the "noise on picture" scenario.

    To stop pirates jumping onto their frequencies! Before they had any elected MPs, the SNP in Scotland used to broadcast Radio Free Scotland on the BBC Channel three audio frequency after closedown....:rolleyes:

  • Interesting, but, if I remember correctly, Radio 4 used to close down and turn the transmitter off and then, the next morning, transmit the tone prior to programmes beginning.

    (I'll also post this in the radio forum).