audio - Stereo "tone-generator" for linux? - Unix & Linux Stack Exchange
Amazon.com: FY6600 2-Channel DDS Arbitrary Waveform Functional Signal Generator Frequency Meter Signal Source Module Frequency Counter 14bits 250MSa/s Sine Square Pulse(60MHz U.S. regulations) : Industrial & Scientific
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Building a simple 2 tone audio generator for testing SSB radios. - YouTube
14 Best Free Signal Generator Software For Windows
Tone Generator Software – Sound Frequency & White Noise Generator (PC or Mac)