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by John Siau March 14, 2017
Monty Montgomery takes us into the lab and uses a series of simple demonstrations to bust some very common myths about digital audio. Test your knowledge of digital audio. This video is fun to watch and easy to understand! Monty takes some difficult concepts and demonstrates them in a clear and simple manner.
Have doubts about Nyquist? Have a fear of stairsteps? Are you worried about ringing? Ever wonder what digital audio does to the timing of transients? This video is for you!
Myth - "Digital audio has stairsteps." (0:00 - 8:40) - Busted! Monty feeds an analog tone into the A/D and produces a continuous analog tone at the output of the D/A. Watch as he examines the output with an analog oscilloscope and an analog spectrum analyzer.
Myth - "Increased bit depths reduce the stairsteps." (8:41 - 9:36) - Busted! The stairsteps were never really there! Samples are impulses not stair steps. This segment also shows that the word length of a dithered digital system determines the signal to noise ratio and NOTHING else!
Myth - "Analog tape has more resolution than digital audio." (9:37 - 11:34) Busted! Tape noise and gaussian dither noise are virtually identical. Cassette tape is equivalent to about 6 bits, and the best studio reel-to-reel tapes are equivalent to about 13 bits.
Myth - "Dither masks quantization noise." (11:35 - 13:50) Busted! Dither replaces quantization distortion with a noise spectrum of our choosing. Harmonic distortion (produced by quantization) is removed by dither and this can be seen on the analog test gear.
Myth - "Signals lower than one LSB cannot be reproduced." (13:37 - 14:08) Busted! Watch a 1/4 LSB tone being transmitted without harmonic distortion through a dithered digital system. Dither gives digital systems an analog amplitude response. The video also shows that dither noise can be shaped to reduce the audibility of the noise (14:08 - 14:55). Monty also shows how dither noise is gradually replaced by distortion as the dither power is reduced (14:55 - 16:09). Noise-shaped dither can use a somewhat lower dither power than gaussian dither, without producing significant distortion (16:09 - 17:18).
Myth - "Digital filters make square waves and impulses ring." (17:19 - 20:52) Busted! The ripples are caused by removing high-frequency harmonics, they are not added by the filter. Monty demonstrates this by passing the same signal through two cascaded A/D-D/A conversions.
Myth - "Digital systems cannot resolve timing between samples." (20:53 - 21:55) Busted! The video shows impulses and square waves passing through an A/D and D/A (analog to digital to analog) while delivering continuous resolution of the timing. The sample rate does not limit the timing resolution! Pay particular attention to the segment between 21:47 and 21:55. The red dots represent the digital sampling instances. Notice how the square wave is accurately reproduced no matter what the phase relationship is to the sampling clock. The phase relationship between the sample clock and the transients in the music has no impact on the wave shape that is reproduced. This is counterintuitive, but clearly demonstrated in this analog to digital to analog pass through an A/D and D/A.
This video was Episode 2. Be sure to watch Episode 1.
Lecture notes on a variety of digital topics - all free! (Good stuff here!)
by John Siau June 06, 2023
At the 2023 AXPONA show in Chicago, I had the opportunity to see and hear the Hill Plasmatronics tweeter. I also had the great pleasure of meeting Dr. Alan Hill, the physicist who invented this unique device.
The plasma driver has no moving parts and no diaphragm. Sound is emitted directly from the thermal expansion and contraction of an electrically sustained plasma. The plasma is generated within a stream of helium gas. In the demonstration, there was a large helium tank on the floor with a sufficient supply for several hours of listening.
While a tank of helium, tubing, high voltage power supplies, and the smell of smoke may not be appropriate for every living room, this was absolutely the best thing I experienced at the show!
- John Siau
by John Siau June 04, 2023
We have added an "Audio Calculators" section to our webpage. Click "Calculators" on the top menu to see more like these:
by John Siau June 03, 2023
If an audio system is composed of multiple components, we may have detailed specifications for each component, but we will not know the performance of the combined system without doing some calculations. You may have questions such as these:
Use Benchmark's online audio calculators to find answers!
For example, if we know the output power of an amplifier, as well as the sensitivity and impedance of our loudspeakers, we can calculate the maximum sound pressure level that our system can produce.
This application note provides interactive examples that help to answer the questions listed above.