Presentation is loading. Please wait.

Presentation is loading. Please wait.

Sound recording and playback

Similar presentations


Presentation on theme: "Sound recording and playback"— Presentation transcript:

1 Sound recording and playback
Angelo Farina 14/12/2012 Sound recording and playback

2 Physical nature of sound
09/13/2003 Origin of Sound: Thermofluidodynamic phenomenon: Particle velocity and variable density of medium (air) Human body can detect sound (p and v) with: ears, but also skin, chest, stomach The trasducers should detect the same quantities 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

3 Transducers: microphones
09/13/2003 From acoustic pressure and particle velocity to physical (electrical) quantities Output signal: voltage (Volts), current (Amperes) or charge (Coulombs) Pressure microphones (related with acoustic pressure) Velocity microphones (related with particle velocity) Hybrid microphones (a proper combination of both quantities) From omnidirectional (100 p and 0 v) to figure of eight (0 p and 100 v) 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

4 Microphone directivity patterns
09/13/2003 Microphone directivity patterns Omnidirectional (100,0) Subcardioid (75,25) Cardioid (50,50) Hypercardioid (25,75) Figure-of-Eight (0, 100) 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

5 Microphones Variable pattern microphone:
09/13/2003 Variable pattern microphone: Neumann U89i variable-pattern microphone 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

6 Sound recording and playback
Cables 09/13/2003 The weak microphone signal (few mV/Pa) has to be amplified and transmitted by means of cables Signal contamination can occur inside the cable, if not properly shielded (balanced) with two opposite-polarity signals Balanced audio cables with XLR connectors (3 pins) 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

7 Sound recording and playback
Preamplifiers 09/13/2003 They should simply amplify the signals, but often they also process the signals: linearly (band pass frequencies), for phantom power supply to mics non-linearly (compression, harmonic distortion) it should be avoided during room acoustics measurements. 2-channels tube microphone preamplifier 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

8 ADC (Analog to Digital Converter)
09/13/2003 ADC (Analog to Digital Converter) Conceptually a black box connecting with two wires: Analog input (sound signal) Digital output (serial digital interface) Two different types of ADCs: PCM converters (Pulse Code Modulation – CD, DAT, DVD) 2. Bitstream converters (DSD, Direct Stream Digital, also called single-bit, employed in SACD). 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

9 ADC (Analog to Digital Converter) 2
09/13/2003 ADC (Analog to Digital Converter) 2 PCM Converters A master clock defines with high precision the instants at which the analog signal has to be “sampled” (Shannon theorem) Applications Resolutions CDs 44100 Hz DAT, DVD Video 48000 Hz DVD audio HD rec. 96000 Hz Special soundcards Hz 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

10 ADC (Analog to Digital Converter) 3
09/13/2003 ADC (Analog to Digital Converter) 3 Low-pass filtering must be applied before entering the ADC, otherwise the signal will be aliased Example: pure tone of 35 kHz Sample rate 48 kHz, Nyquist freq. 24 kHz, difference = 11 kHz After digital conversion will be 13 kHz (i.e kHz) Solution: low-pass antialiasing filters, oversampling 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

11 ADC (Analog to Digital Converter) 4
09/13/2003 ADC (Analog to Digital Converter) 4 Also vertical axis (amplitude) is discretized. Typical resolutions: 16 bits; 20 bits; (24 bits) Example: maximum voltage +5V Discretization with 16 bit (32767 steps) means 90 dB Discretization with 20 bit ( steps) means 114 dB High-end, 2-channels ADC unit (24 bits, 192 kHz, Firewire interface) 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

12 ADC (Analog to Digital Converter) 5
09/13/2003 ADC (Analog to Digital Converter) 5 Bitstream Converters The idea arises from oversampling: increasing sample frequency it would be possible to increase amplitude resolution (bits) Sample rate: 2.88 MHz and 1 bit resolution: dividing to 2 for 6 time is equivalent to CD audio sample rate, but only with 7 bits! In order to enhance high freq. resolution, a proper noise shaping of high order is required, suitable for static (non transient) signals. Below 88 Hz the Bitstream converters outperform PCM conv. 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

13 ADC (Analog to Digital Converter) 6
09/13/2003 ADC (Analog to Digital Converter) 6 Bitstream Converters The Bitstream converters are widely employed with SACD system (Super Audio CD), co-developed by Sony and Philips. However they are much more expensive that 24 bit 96 kHz PCM a low-cost multichannel USB-2 soundcard, equipped with 2 microphone preamps 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

14 Digital Signal Processing
09/13/2003 Digital Signal Processing Waveform editors sampled waveform displayed as amplitude vs time (time domain) 14/12/2012 Sound recording and playback AES 115th Convention - New York, NY

15 Recording/playback methods
Mono followed by amplitude panning (stereo or surround) Stereo (ORTF on 2 standard loudspeakers at +/- 30°) Discrete ITU 5.1 (from different 5-mikes layouts) Full 3D Ambisonics 1st order (decoding the B-format signal) 2D Ambisonics 3rd order (from Mark Poletti’s circular array microphone) Wave Field Synthesis (from the circular array of Soundfield microphones) Hybrid methods (Ambiophonics) HOA (high order Ambisonics, Eigenmike) SPS (Spatial PCM Sampling) 14/12/2012 Sound recording and playback

16 Traditional “surround” – amplitude panning
MIX 5 ch. 5 ch. 5 ch. 1 ch. 1 ch. 5 ch. Surround panner Each mono track is positioned artificially, by means of “pairwise” or “advanced” amplitide panning 14/12/2012 Sound recording and playback

17 Sound recording and playback
Panning laws Instead of just feeding a single loudspeaker with each mono track, it is advantageous to “pan” each signal ver two or more loudspeakers “Pairwise Panning” with constant power- each signal is always sent to just 2 loudspeakers Peter Craven’s Ambisonics panning at 5th order – all the loudspeakers are always fed 14/12/2012 Sound recording and playback

18 Peter Craven’s panning
Panning laws An alternative display of teh spanning laws is by charting the polar patterns of a number of “virtual microphones”, each feeding the corresponding loudspeaker “Pairwise Panning” Peter Craven’s panning 14/12/2012 Sound recording and playback

19 Sound recording and playback
ORTF Stereo 60° 2 Microphones 2 Loudspeakers Playback occurs over a pair of loudspeakers, in the standard configuration at angles of +/- 30°, each being fed by the signal of the corresponding microphone 14/12/2012 Sound recording and playback

20 Binaural (Stereo Dipole)
Original 2-channels recording of the signals coming from N sources xr xl Cross-talk canceller dNr N dNl 3 d2r 20° 2 d2l d1r 1 d1l Reproduction occurs over 2 loudspeakers angled at +/- 10°, being fed through a “cross-talk cancellation” digital filtering system 14/12/2012 Sound recording and playback

21 Binaural (Stereo Dipole#2)
14/12/2012 Sound recording and playback

22 Binaural (Stereo Dipole#3)
hll hlr hrl hrr fll flr frl frr 14/12/2012 Sound recording and playback

23 Binaural (Dual Stereo Dipole)
Scheme advantages: 3D sound reproduction Rotating of the head The cross-talk filters could equalise also the loudspeakers disadvantages: Low frequencies Coloration outside the “sweet spot” Subwoofer 14/12/2012 Sound recording and playback

24 Binaural (Dual Stereo Dipole#2)
Frontal Rear Quested 2108 monitors Quested F11P monitors 14/12/2012 Sound recording and playback

25 “Discrete” microphone arrays
Many different geometrical layouts were proposed – each microphone feeds the corresponding loudspeaker 14/12/2012 Sound recording and playback

26 “Discrete” microphone arrays
In a discrete system, each microphone feeds just the corresponding loudspeaker: Microfoni Altoparlanti 14/12/2012 Sound recording and playback

27 “Discrete” microphone arrays
Williams MMA INA-5 Schema del sistema microfonico Williams MMA C : Cardioide, 0° L, R : Cardioide, ± 40° LS, RS : Cardioide, ± 120° Schema del sistema microfonico INA-5 C : Cardioide, 0° L, R : Cardioide, ± 90° LS, RS : Cardioide, ± 150° 14/12/2012 Sound recording and playback

28 Sound recording and playback
ITU 5.1 surround OCT Schematic of the setup C : Cardioid, 0° L, R : Super Cardioid, ± 90° LS, RS : Cardioid, ± 180° 14/12/2012 Sound recording and playback

29 “Discrete” microphone arrays
Why such a limited success? Little control during recording and during post-processing Fixed angle of covering, which cannot be adjusted after the recording is done It makes it difficult to add to the recording the sound track of separately-recorded voices or instruments Currently available directivity patterns of first-order microphones do not correspond with the ideal, asymmetrical patterns implemented by optimal panning laws. 14/12/2012 Sound recording and playback

30 Ambisonics 3D (1st order)
Reproduction occurs over an array of 8-24 loudspeakers, through an Ambisonics decoder 14/12/2012 Sound recording and playback

31 3D extension of the pressure-velocity measurements
The Soundfield microphone allows for simultaneous measurements of the omnidirectional pressure and of the three cartesian components of particle velocity (figure-of-8 patterns) 14/12/2012 Sound recording and playback

32 Directivity of transducers
Soundfield ST-250 microphone 14/12/2012 Sound recording and playback

33 A-format microphone arrays
Today several alternatives to Soundfield microphones do exists. All of them are providing “raw” signals from the 4 capsules, and the conversion from these signals (A-format) to the standard Ambisonic signals (B-format) is performed digitally by means of software running on the computer 14/12/2012 Sound recording and playback

34 Sound recording and playback
Ambisonics decoding Each speaker fed is just obtained as a weighted sum of the 4 B-format signals (WXYZ) The weighting factors only depend on the position of each loudspeaker It is possible to add a small FIR filter for matching perfectly the gain and phase of all loudspeakers 14/12/2012 Sound recording and playback

35 Ambisonics decoding advantages: Bi-square Ambisonics array
Tridimensional Good later sound perception Good bass response Wide “sweet spot”, no colouring outside it disadvantages: Not isotropic Advanced decoding required (Y gets more weight than X and Z, and this must be compensated for) Bi-square Ambisonics array 14/12/2012 Sound recording and playback

36 Bi-square Ambisonics array
Front-Right Down-Right Up-Right 8 Turbosound Impact 50 loudspeakers: Light, easily fixed and oriented Good frequency response Very little distortion 14/12/2012 Sound recording and playback

37 Sistema DSP per decoding Ambisonics
BSS Soundweb 9088-II (8 ins, 8 outs) SID Futureclient fanless PC (Pentium-III 1 GHz) 14/12/2012 Sound recording and playback

38 Programmazione del decoder sul processore digitale SoundWeb
14/12/2012 Sound recording and playback

39 Effetto dell’equalizzazione FIR di ciascun altoparlante
Funzione di tarsferimento misurata dell’altoparlante Front-left Filtro inverso a fase minima (100 coefficienti) Effetto equalizzante del filtro 14/12/2012 Sound recording and playback

40 Decoder Ambisonics via software
Audiomulch VST host Gerzonic bPlayer Gerzonic Emigrator 14/12/2012 Sound recording and playback

41 Sound recording and playback
Sale Ambisonics 3D ASK – Reggio Emilia University of Ferrara University of Bologna 14/12/2012 Sound recording and playback

42 Sistema di gestione audio completo
Philips 15” Brilliance LCD display Logitech wireless keyboard & mouse Echo Layla Soundboard (8 ins, 10 outs) BSS Soundweb digital processor 2 Crown K1 amplifiers QSC CX168 8-channels amplifier Signum Data Futureclient fanless PC 14/12/2012 Sound recording and playback

43 Metodi ibridi (Ambiophonics)
Sistema Ambiophonics 3D (10 altoparlanti): 14/12/2012 Sound recording and playback

44 Sound recording and playback
Ambiophonics In sostanza, vengono impiegati simultaneamente il sistema Ambisonics e gli Stereo-Dipoles 14/12/2012 Sound recording and playback


Download ppt "Sound recording and playback"

Similar presentations


Ads by Google