Sound Recording – Choosing the Optimal Frequency

Sound Recording – Choosing the Optimal Frequency

Acoustic is the most challenging aspect of producing professional sound recording. When your sound recording acoustic is bad, it will totally affect the whole sound. There are many inexpensive things you can do to produce great sound.

It is very important to have good acoustic material since vibrations in the air create sounds. Acoustic is usually affected by the frequency level. A good way to test the sound recording acoustics is through a sine wave of 4 to 6 kHz.
 

Within the video world, sounds often get given the backbench, while the concepts of overdubbing and ADR are entirely welcomed, although the inability to capture audio correctly makes them redundant. Sound set up has many variables that must be taken into consideration. This article is practically about sample frequency, which is one of sound’s parameters that must be considered.

1. Detailing Concepts

The number of audio samples per second is known as sample rate. It is measured in Hz or kHz. In an audio dream, the difference between the highest and the lowest frequency is known as bandwidth. The maximum audio frequency that can be reproduced is determined by sample rate. Practically, sample rate is twice the maximum frequency known as Nyquist frequency.

 

The number of possible amplitude you can record for each sample is determined by the bit depth. There are different depths, but the most common ones are 16-bit, 24-bit, and 32-bit. The bits represent a number of possible values and are all binary terms. Possible values that are expressed are:

 

  • 16-bit – 65, 536 values
  • 24-bit – 16,777,216 values
  • 32-bit – 4,294,967,296 values

2. What is the significance of sampling frequency to sound recording?

A signal can be completely reconstructed from a series of evenly spaced measurements, or samples, provided that the signal contains no frequencies higher than half the sampling rate. The limiting frequency-half the sample rate-is called the Nyquist frequency.

Sampling frequency helps to determine the frequency range in the form of a digital waveform. A broad range of frequencies can be represented by waveforms samples at a high-frequency rate. Sampling frequency helps to determine the maximum bandwidth of a sample waveform. A sine wave sampled at 24, 000 Hz represent all frequencies up to its Nyquist frequency of 12, 000 Hz.

When a signal to be sampled has energy at frequencies above Nyquist, a problem called aliasing occurs. Therefore, it occurs when the sampling frequency is much too low for the frequency of an input signal.

Aliasing can produce sounds of lower frequency from sounds that are higher in frequency above Nyquist. After its occurrence, it will be hard to distinguish a component generated by aliasing from the one present in the input signal. In the digitized waveform, this effect is one of the most common sources of distortion.

3. Quantization

Quantization is another important limitation suggested by the Sampling frequency in the measurement of each sample. The accuracy of this measurement, or quantization, is dependent on the number of bits allocated to the samples. The more bits we allocate, the longer the word length and the more accurate the measurement.
 
As analog audio enters the A/D converter, a small amount of noise is added to the signal to prevent harmonic distortion caused by quantization error. The signal then passes through a low pass filter to eliminate all frequency components above half the sample rate. The signal then arrives at the sample and hold circuit, which captures the voltage and holds it as it is measured by the successive approximation circuit. The voltage is compared to a relatively large reference voltage, and a 1 or 0 is recorded, depending on that comparison. The voltage is held by the sample and hold circuit is then compared against a combination of successively smaller reference voltages, with 1s and 0s being recorded at each iteration. When the process is done, a 16-bit and a 24-bit word have been captured to represent the signal’s voltage at that point in time. This entire process happens at each tick of the sample clock.
 
 When analog signals are transformed into digital signals, the quality of the signal is inevitably lost. It all depends on the sampling frequency. When it is very high, the quality produced will be all good. It means that there is a direct relationship between frequency and quality.

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