Sound card

A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term sound card is also applied to external audio interfaces used for professional audio applications. Sound functionality can also be integrated onto the motherboard, using components similar to those found on plug-in cards. The integrated sound system is often still referred to as a sound card. Sound processing hardware is also present on modern video cards with HDMI to output sound along with the video using that connector; previously they used a S/PDIF connection to the motherboard or sound card. Typical uses of sound cards or sound card functionality include providing the audio component for multimedia applications such as music composition, editing video or audio, presentation, education and entertainment (games) and video projection. Sound cards are also used for computer-based communication such as voice over IP and teleconferencing. Sound cards use a digital-to-analog converter (DAC), which converts recorded or generated digital signal data into an analog format. The output signal is connected to an amplifier, headphones, or external device using standard interconnects, such as a TRS phone connector. A common external connector is the microphone connector. Input through a microphone connector can be used, for example, by speech recognition or voice over IP applications. Most sound cards have a line in connector for an analog input from a sound source that has higher voltage levels than a microphone. In either case, the sound card uses an analog-to-digital converter (ADC) to digitize this signal. Some cards include a sound chip to support the production of synthesized sounds, usually for real-time generation of music and sound effects using minimal data and CPU time. The card may use direct memory access to transfer the samples to and from main memory, from where a recording and playback software may read and write it to the hard disk for storage, editing, or further processing.

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USBFuzz: A Framework for Fuzzing USB Drivers by Device Emulation

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The Universal Serial Bus (USB) connects external devices to a host. This interface exposes the OS kernels and device drivers to attacks by malicious devices. Unfortunately, kernels and drivers were developed under a security model that implicitly trusts connected devices. Drivers expect faulty hardware but not malicious attacks. Similarly, security testing drivers is challenging as input must cross the hardware/software barrier. Fuzzing, the most widely used bug finding technique, relies on providing random data to programs. However, fuzzing device drivers is challenging due to the difficulty in crossing the hardware/software barrier and providing random device data to the driver under test. We present USBFuzz, a portable, flexible, and modular framework for fuzz testing USB drivers. At its core, USBFuzz uses a software-emulated USB device to provide random device data to drivers (when they perform IO operations). As the emulated USB device works at the device level, porting it to other platforms is straight-forward. Using the USBFuzz framework, we apply (i) coverage-guided fuzzing to a broad range of USB drivers in the Linux kernel; (ii) dumb fuzzing in FreeBSD, MacOS, and Windows through cross-pollination seeded by the Linux inputs; and (iii) focused fuzzing of a USB webcam driver. USBFuzz discovered a total of 26 new bugs, including 16 memory bugs of high security impact in various Linux subsystems (USB core, USB sound, and network), one bug in FreeBSD, three in MacOS (two resulting in an unplanned reboot and one freezing the system), and four in Windows 8 and Windows 10 (resulting in Blue Screens of Death), and one bug in the Linux USB host controller driver and another one in a USB camera driver. From the Linux bugs, we have fixed and upstreamed 11 bugs and received 10 CVEs.

USENIX ASSOC2020

Sound card

Frequency modulation synthesis

Frequency modulation synthesis (or FM synthesis) is a form of sound synthesis whereby the frequency of a waveform is changed by modulating its frequency with a modulator. The (instantaneous) frequency of an oscillator is altered in accordance with the amplitude of a modulating signal. FM synthesis can create both harmonic and inharmonic sounds. To synthesize harmonic sounds, the modulating signal must have a harmonic relationship to the original carrier signal. As the amount of frequency modulation increases, the sound grows progressively complex.

Digital audio

Digital audio is a representation of sound recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is typically encoded as numerical samples in a continuous sequence. For example, in CD audio, samples are taken 44,100 times per second, each with 16-bit sample depth. Digital audio is also the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form.

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