Heinrich Rudolf Hertz - 155th Birthday

Well would be but sadly died at the age of 36! But didn't take him long to see what everyone else couldn't.

Im sure you have guess the young German electronic engineer and physicist who clarified and expanded the electromagnetic theory of light introduced by James Maxwell publishing his theory in 1865. Maxwell was also phenomenal is creating a theory from seemingly unrelated experiments and studies of electricity, magnetism and optics and combined them. He was also known for the first durable colour photograph earlier in 1861 and even did foundation work on rigidity for bridges, and is considered one of the greatest physicists of all time.

Back to our friend Heinrich Rudolf Hertz. He was the first to prove with immense certainty the presents of electromagnetic waves by designing and engineering instruments to transmit and receive radio pulses using procedures to discredit other sources of wireless phenomenon. As such his name was given to the unit of frequency known as, you guessed it Hertz (Hz)

Just So I Don't Breech Copyright :)

See a better image of him from Wikipedia

Dither and Quantization Error

Dither is an internationally applied form of noise used to randomize quantization error, preventing large scale patterns such as "banding" in images. 

Example of image "Banding"

Dither is routinely used to processing both digital audio and digital video data and usually one of the last stages in post production for compact discs. 

Quantization Error is the difference in the actual analog value and the quantized digital value. This is due to either rounding of digital views or truncation. The error is sometimes considered as an additional random signal called quantization noise because of its "stochastic" or non-deterministic behavior

Cheers Guys,

Matt Price

Sampling theorem

The Nyquist–Shannon sampling theorem, after Harry Nyquist and Claude Shannon, is a fundamental result in the field of information theory, in particular telecommunications and signal processing. Sampling is the process of converting a signal(for example, a function of continuous time or space) into a numeric sequence (a function of discrete time or space).

Sampling theorem which in essence shows that a bandlimited analog signal can be reconstructed perfectly from an infinite sequence of samples if the sample rate exceeds 2B samples per second. B is the highest frequency in the original signal. If the signal contains components at exactly B hertz, then samples spaced 1/(2B) seconds do NOT completely determine the signal.

E.g. 20,000 Hertz into this forumla will not be reconstructed perfectly at anything less than 0.00003 seconds per sample. Recording at a sample rate of 48kHz is sampling at 0.00002 seconds per sample, hence for situations like recording dialogue where the highest frequency for normal conversation is below 20kHz (because we can't hear higher).

Possibly Useful Drawing of a 2hz sine wave

So in recording effects if you wanted to have flexibility to manipulate then you can record at 192kHz and then the spacing is 1 sample every 0.0000052083 of a second, this is useful for slowing down samples more effectively than less samples.

This is again like most perfect theories based on a perfect world and so is an approximate in our not so perfect world.

Hope this ended up making sense.

Thanks,

Matt Price

Q+A: Sample rates explained....

Sample rate is the number of samples per unit of time taken from a continuous signal to make a discrete signal, the unit of sample rates are Hertz. We record a discrete signal because we only need lots of little samples of the signal to track how loud it is etc... So the higher the samples the more of these measurements are taken per second. The standard for recording dialogue is 48kHz (48,000 hz) or 44.1kHz and unless your playing on really nice speakers you really wont be able to tell the difference.

For some sound effects recording people record at 192kHz which has advantages for slowing effects down and manipulating them. Also higher sample rates help prevent aliasing, which refers to an effect that causes different signals to become indistinguishable 


also see: Bit Depth

Thanks,

- Matt Price

Q+A: Basic Sound Questions...

This is going back to basics with what is sound anyway?...


What is sound and how is it created?
Sound is a vibration and/or a wave of air molecules caused by motion of an object. This wave is a compression wave where the molecules are bunched up like a wave in the sea, A sound wave is created when a series of these pressure changes/waves move through the air. This wave or waves speed depends on the temperature, e.g. at 15 degrees Celsius the speed is 340.276 m/s but at 25C the speed is 346.13 m/s. (Calculator here).


Through solids the wave will bounce back or echo/reverberate and the energy can change from acoustical to electrical energy which is how microphones and telephones are able to work.


What is frequency?
When drawing a sound wave, like with any wave there is a peak and a valley which vary in distance from each other. Sound sources vibrate at different rates or frequencies as they move through the air. We measure frequency in cycles per second or Hertz. This is named after Heinrich Rudolf Hertz (February 22, 1857 – January 1, 1894) who was a German physicist who was the first to satisfactorily demonstrate the existence of electromagnetic waves by building an apparatus to produce and detect VHF or UHF radio waves.
The faster an object vibrates the higher the frequency and thus higher the pitch of the sound. a common example is a tuning fork for A above middle C will vibrate at 440 times per second and so has a frequency of 440 Hertz.




What is amplitude? 
We already understand by now that sound is made by pushing air molecules together in varying degrees of strength, this is amplitude. for example if something is struck really hard the wave will carry some of that energy through the air and it will sound louder than if it is struck gently. Sound waves with the same frequency can have different amplitudes.


Feel free to add any comments if i haven't covered anything in enough detail.


Thanks,


- Matt Price