Undetectable combining of nonaligned concurrent signals

摘要

The approach shown provides for an efficient implementation of time response, level response and frequency response alignment between two audio sources such as DAB and FM that may be time offset from each other by as much as 2 seconds, and produces an aurally undetectable transition between the sources. Computational load is significantly reduced over the approaches known in the prior art.

主权项

1. An apparatus for blending of a Digital Audio Broadcast transmission first audio signal and a Frequency Modulated transmission second audio signal comprising:
a first receiver receiving a Digital Audio Broadcast transmission; a first demodulator connected to said first receiver producing a first left audio signal and a first right audio signal from said received Digital Audio Broadcast transmission; a second receiver receiving a Frequency Modulated transmission; a second demodulator connected to said second receiver producing a second left audio signal and a second right audio signal from said received Frequency Modulated transmission; a quality of service unit connected to said first receiver, said first demodulator, said second receiver and said second demodulator, said quality of service unit producing a first quality of service indication for said received Digital Audio Broadcast transmission and a second quality of service indication for said received Frequency Modulated transmission; and a blending unit receiving said first left audio signal and said first right audio signal from said first demodulator, said second left audio signal and said second right audio signal from said second modulator and said first quality of service indication and said second quality of service indication from said quality of service unit, said blending unit operable to
calculate an average envelop value of the first audio said over a time span Ts as follows:
DAB audio=DAB_Left+DAB_Right,DAB_envelope=ABS[DAB_audio], andDAB_Envelope_Avg=(1−α)*DAB_Envelope_Avg+α*DAB_envelope, where: DAB_Left is said left channel of said first audio signal; DAB_Right is said right channel of said first audio signal; and α is selected whereby Ts*(1−α)/α˜0.1;
downsample the average envelop value of said first audio signal;calculate an average envelop value of said second audio signal over the time span Ts as follows:
FM_audio=FM_Left+FM_Right,FM_envelope=ABS[FM_audio], andFM_Envelope_Avg=(1−α)*FM_Envelope_Avg+α*FM_envelope, where: FM_Left is said left channel of said second audio signal; and FM_Right is said right channel of said second audio signal;
downsample the average envelop value of said second audio signal;calculate a first gain adjustment for said first audio signal;calculate a second gain adjustment for said second audio signal;apply gain adjustment to said second audio signal;calculate a time delay between said first audio signal and said second audio signal; andblend said first audio signal and said second audio signal offset by said calculated time delay based upon said first Quality of Service indication and said second Quality of Service indication.