vfcc digital audio

Digital Audio : 

Digital Audio

Analog versus Digital Recording : 

Analog versus Digital Recording Analog Recording Series of magnetic fluctuations on tape Analogous to the acoustical vibrations of the source Digital Recording Numerically encoded measurements of an electronic signal The output of a transducer (e.g., microphone) is translated to binary code The binary code is stored and retrieved from various media Digital Audio Tape (DAT) Compact Disc (CD), Digital Versatile Disc (DVD) Floppy Disc, Zip Disc, Flash RAM Hard Disk Drive (HDD)

Digital Recording Process : 

Digital Recording Process An analog signal is transduced into an electrical signal The electrical signal is converted by the ADC Binary Code is recorded onto the digital media

PCM : 

PCM Pulse-Code Modulation A digital representation of an analog signal “uncompressed” digital audio File Formats Wave Microsoft Windows format (.wav) Broadcast Wave format - BWF (.wav) Standard for most DAW’s Incorporate metadata and time-code related positioning information AIFF Audio Interchange File format (.aiff)

Digital Recording Quality : 

Digital Recording Quality The quality of a Digital recording is based on two basic principles: Sample Rate (number of “snapshots” per second BIT Depth (number of values assigned to amplitude

Sample and Sample Rate : 

Sample and Sample Rate SAMPLE - Represents a snapshot of the signal in time The SAMPLE RATE is the number of samples that can be taken in a given time period, usually defined as one second. A digital system’s ability to reproduce sound improves as the sample rate increases (because more snapshots are available).

DAC’s and Samples : 

DAC’s and Samples An analog waveform: Digital Representation:

Relative Sample Rates : 

Relative Sample Rates Three relative sample rates applied to the same analog signal: Low Sample Rate: Moderate Sample Rate: High Sample Rate: Increasing Quality

The Nyquist Theory : 

The Nyquist Theory How do we determine the appropriate ratio of sample rate and quality? Scientist/Inventor Harry Nyquist noted that the sample rate must be twice that of the highest frequency to be recorded. Range of human hearing? 20 Hz - 20 kHz (20,000 Hz) If 20 kHz is the highest (the Nyquist Frequency), what would sample rate need to be? 40 kHz (40,000 samples/cycles per second)

Alias and Aliasing/Foldover : 

Alias and Aliasing/Foldover High frequency pitches include overtones that go beyond 20 kHz They effect the perception of the fundamental. A sample rate of 40 kHz is not sufficient to accurately capture frequencies above 20 kHz. Aliasing will occur An ALIAS is a digital artifact that is caused by pitches outside of the sample rate’s ability to record pitches accurately. ALIASING, is a type of digital noise or distortion caused by the presence of aliases.

Aliasing/Foldover : 

Aliasing/Foldover If a low sample rate, such as 800 Hz (samples per second) is used, the Nyquist Theorem states that only pitches 400 Hz and lower can be recorded accurately. 800 Hz is sufficient to represent 150 Hz: But not to represent 600 Hz: The result of sampling 600 Hz with a sampling rate of 800 Hz is an alias of 200 Hz: Video of aliasing Sample: aliasing

Standard Sampling Rates : 

Standard Sampling Rates How is aliasing dealt with? Low-Pass Filter on the input of a ADC Cut-off Frequency is set to the highest frequency in the signal that is to pass undisturbed. Sampling Rate standard for CD’s is 44.1 kHz (44,100 Hz) 22,050 Hz 48 kHz is standard sampling rate for DVD’s and DAT’s Other sampling rates: 88.2 kHz, 96 kHz, 192 kHz

Bit Depth : 

Bit Depth Higher sampling rates will increase the frequency range Higher Bit Depth (Word Length) will increase the dynamic range Each number is encoded as a binary number by the ADC. This process is called QUANTIZATION

Quantization : 

Quantization In Quantization, the actual amplitude of the analog signal is rounded off to the closest value that the A/DC can represent. QUANTIZATION ERROR refers to the difference between the actual value and the rounded value. QUANTIZATION NOISE the result of cumulative errors.

Signal-to-Noise Ratio : 

Signal-to-Noise Ratio SIGNAL-to-NOISE RATIO a system’s ability to not distort The range of binary numbers must be as high as possible so that the amplitude can be measured as accurately as possible and to have the highest possible S-to-N Ratio The number of bits x 6 will indicate maximum dB level of the signal that can be played without distortion.

Critical Listening : 

Critical Listening Is analog recording better or worse than digital recording?