International call progress tones for IP-PBX and VoIP telephony

Telephone Line Signalling

Howler tone

  • A tone used in older exchanges to inform a subscriber that their receiver is off-hook.
  • It is a tone that may be swept in pitch and/or incremented in volume over a few seconds.
  • This tone has been superceeded by the Off-hook warning tone.

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Related product: CPT-Master tone generator app