Audio analyzer
Encyclopedia
Audio Analyzer is a type of test instrument to measure the quality of audio signal. A high quality audio signal has low noise and distortion.
An audio Analyzer testing is done on a stimulus-response basis, i.e. a test stimulus signal with known specifications is injected into the input of a device under test (DUT) and the output signal of the DUT is tested by Audio Analyzer. The performance of the DUT is evaluated by comparing the output signal with the known input signal.
So, a typical Audio Analyzer consists of a source (to generate the stimulus signals) and an analyzer (to implement the measurements).
The industry first audio source HP200A
was introduced in 1939 by HP Company. Since then, Audio Analyzer is used in broader industries for product design, performance verification, trouble shooting and maintenance. For example a design engineer wants to test the performance of an amplifier circuit; a production engineer wants to test audio quality of an iPad.
The popular audio analyzer models include: AP2722 (Audio Precision), HP8903B (HP/Agilent), U8903A (Agilent) and UPV (Rohde & Schwarz).
The most important specs for signal source include waveforms, frequency range, amplitude range, residual distortion and noise, absolute accuracy of amplitude, absolute accuracy of frequency and features such as selectable impedances, balanced/unbalanced configuration, coupling, user interface etc.
The most important specs for analyzer include measurement bandwidth, amplitude range, inherent distortion and noise, absolute accuracy of amplitude, absolute accuracy of frequency and features such as selectable impedances, balanced/unbalanced configuration, coupling, user interface etc.
is required for most of audio measurements. An audio filter is designed to pass some region of signals and reject others in a specified frequency section. Frequently used filters are low pass filter, High pass filter and Weighting filters.
Connector type of analog audio: XLR (balance or Common mode), BNC (Unbalance).
Connector type of digital audio: XLR (Balance), BNC (Unbalance), Optical (Toslink), D-Sub 25 connector (I2S, DSP, Left Justified and Right Justified.).
An audio Analyzer testing is done on a stimulus-response basis, i.e. a test stimulus signal with known specifications is injected into the input of a device under test (DUT) and the output signal of the DUT is tested by Audio Analyzer. The performance of the DUT is evaluated by comparing the output signal with the known input signal.
So, a typical Audio Analyzer consists of a source (to generate the stimulus signals) and an analyzer (to implement the measurements).
The industry first audio source HP200A
HP200A
The HP200A was the first product made by Hewlett-Packard and was manufactured in David Packard's garage in Palo Alto, California.It was a low-distortion audio oscillator used for testing sound equipment. It used the Wien bridge oscillator circuit, which had been the subject of Bill Hewlett's...
was introduced in 1939 by HP Company. Since then, Audio Analyzer is used in broader industries for product design, performance verification, trouble shooting and maintenance. For example a design engineer wants to test the performance of an amplifier circuit; a production engineer wants to test audio quality of an iPad.
The popular audio analyzer models include: AP2722 (Audio Precision), HP8903B (HP/Agilent), U8903A (Agilent) and UPV (Rohde & Schwarz).
Audio Source
An audio source can generate several signal waveforms: sine wave, dual sine waves, square, inter-modulation waveform (SMPTE IMD, DFD), noise, multitone, DC and arbitrary waveform.The most important specs for signal source include waveforms, frequency range, amplitude range, residual distortion and noise, absolute accuracy of amplitude, absolute accuracy of frequency and features such as selectable impedances, balanced/unbalanced configuration, coupling, user interface etc.
Audio Analyzer
An audio analyzer implements measurements. It is a system, consisting of a series of precision testers and measurement software:AC/DC volt meter, frequency counter, noise figure meter, distortion meter, spectrum analyzer, oscilloscope, audio frequency sweeper.The most important specs for analyzer include measurement bandwidth, amplitude range, inherent distortion and noise, absolute accuracy of amplitude, absolute accuracy of frequency and features such as selectable impedances, balanced/unbalanced configuration, coupling, user interface etc.
Filters
FilterFilter
- Chemistry, engineering and materials :In chemistry, engineering, or household usage, a device to separate mixtures. See:* Filter , critical components of both freshwater and marine aquaria...
is required for most of audio measurements. An audio filter is designed to pass some region of signals and reject others in a specified frequency section. Frequently used filters are low pass filter, High pass filter and Weighting filters.
- Low-pass filterLow-pass filterA low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
• 15 kHz low pass • 20 kHz low pass • 30 kHz low pass • 80 kHz low pass •User-defined - High-pass filterHigh-pass filterA high-pass filter is a device that passes high frequencies and attenuates frequencies lower than its cutoff frequency. A high-pass filter is usually modeled as a linear time-invariant system...
• 20 Hz high pass • 100 Hz high pass • 400 Hz high pass • User-defined - Weighting filterWeighting filterA weighting filter is used to emphasise or suppress some aspects of a phenomenon compared to others, for measurement or other purposes.- Audio applications :...
• A Weighting (ANSI-IEC “A” weighted, per IEC Rec 179) • CCIR 1K weighted (CCIR Rec. 468) • CCIR 2K weighted (Dolby 2K) • C-Message (C-Message per IEEE 743) • CCITT (ITU-T Rec. O.41, ITU-T Rec. P.53) • User-defined - Level/amplitude measurement: To measure the AC/DC level with the different type of detectors (RMS, Peak and Quasi Peak detectors).
- Frequency Measurement: To measure the frequency of the signal to be tested.
- Phase Measurement: The phase difference of 2 signals. The phase measurement requires that analyzer has at least 2 input channels.
- THD+N: Signal’s total harmonic distortion + noise.
- SINADSINADSINAD stands for Signal-to-noise and distortion ratio. It is a measure of the quality of a signal from a communications device, often defined as:...
: -20log (THD+N) - Inter-modulation Distortion: The distortion caused by two or more signals of different frequencies being mixed together. The most frequency used inter-modulations standards are SMPTE IMD and DFD.
- NoiseNoiseIn common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise heard when listening to a weak radio transmission with significant electrical noise...
: The noise level or ratio of the signal to be tested. It is the portion of which signal fundamental and its harmonic are removed from the signal to be tested. - SNRSNRThe initialism SNR may refer to:* Signal-to-noise ratio* Supernova remnant* Sporting News Radio...
: The signal to noise ratio. - Crosstalk: To measure signal leakage from one channel to another.
- Sweep Measurement: To evaluate the audio measurement by sweeping frequency or amplitude. The frequently used sweeping measurement is frequency vs. level response which evaluates the DUT’s level change in different frequency points.
- Frequency domain measurement: This is spectrum analyzer display of signal. A frequency domain representation is a graph of amplitude versus frequency.
- Time domain measurement: This is oscilloscope display of signal. A time domain representation is a graph of amplitude versus time
Analog audio and digital audio
- Analog audio: Most of audio signals are analog signal which you can hear with your ears by connecting a earphone or speaker. Analog audio is a representation of the intensities of audio signal in voltages on a wire.
Connector type of analog audio: XLR (balance or Common mode), BNC (Unbalance).
- Digital AudioDigital audioDigital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...
: With digital signal processing technology (DSP) is getting popular, engineers find that it is much easier to process audio signal digitally. Digital audio is to uses a digit or number to describe audio signal. Some popular digital audio formats are: S/PDIF, AES3, Toslink, I2S, DSP, Left Justified and Right Justified.
Connector type of digital audio: XLR (Balance), BNC (Unbalance), Optical (Toslink), D-Sub 25 connector (I2S, DSP, Left Justified and Right Justified.).
- I2S, or Inter-IC Sound, is an electrical bus interface standard used for connecting digital audio devices together. It is most commonly used to carry PCM information between the CD transport and the DAC in a CD player.
- S/PDIFS/PDIFS/PDIF is a digital audio interconnect used in consumer audio equipment over relatively short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fiber optic cable with TOSLINK connectors. S/PDIF interconnects components in home theaters and other digital high...
(Sony/Philips Digital InterFace), A serial interface for transferring digital audio between devices such as CD and DVD players and amplifiers. - AES3 or AES/EBU (American Engineering Society/European Broadcasting Union) A serial interface for transferring digital audio between devices such as CD and DVD players and amplifiers.
Reference
- Understanding the Decibel in Audio Measurements
- SINAD measurements Using Audio Analyzer
- Two-Way Radio Testing with Audio Analyzer
- Migrating Code from the HP8903B to the U8903A