Database for HF Transmitted Speech with Carrier Frequency Difference

This public database is designed for evaluation of carrier frequency difference estimation systems and is published as part of our paper "Open Range Pitch tracking for Carrier Frequency Difference
Estimation from HF Transmitted Speech". It consists of over 23 ours of real transmissions over HF links with a known carrier frequency shift during demodulation.

To record the data we have set up a transmission system between our base station in Paderborn and several other distant base stations across Europe (see Fig. 4), transmitting utterances from the LibriSpeech corpus.

Kiwi-software defined radio (SDR) devices at distant base stations were utilized to demodulate the received SSB HF signals and send the recorded audio signals back to our servers via a websocket connection. Audio markers had been added to the transmitted signal to allow for an automated time alignment between the transmitted
and received signals, easing the annotation and segmentation of the data.
For the transmissions a beacon, callsign DB0UPB, was used, which was supervised by a human to avoid interference with other ham radio stations. The HF signals are SSB modulated using the Lower Side Band (LSB) with a bandwidth of 2.7 kHz at carrier frequencies of 7.06 MHz − 7.063 MHz and 3.6 MHz − 3.62 MHz. To simulate a carrier frequency  difference the demodulation frequency of the transmitter and the receiver were selected to differ by values from the  set [0, 100, 300, 500, 1000]. Although the original speech samples have a sampling rate of 16 kHz, and the  Kiwi-SDR samples the data at 12.001 Hz, the finally emitted data is band-limited to 2.7 kHz (International Telecommunication Union (ITU) regulations) which introduces a loss of the upper frequencies in case of LSB
transmission depending on the carrier frequency difference. The data set has a total size of 23:31 hours of which 3:28 hours contain speech activity.