Hexaphonic Digital Mixer

1
Hexaphonic Digital Mixer

• December 11, 2003

2
Group 14 Members

• Thomas Kennedy (Group Leader)
• Jonathan Maikisch
• Joseph Keller
• Ali PourManouchehri
• Advisor Prof. Hong Man

3
Sponsors

• Tom and Terri Kennedy

4
Abstract

• Geared toward live DJs
• Implementation of current and new technologies to
  a rapidly developing niche market
• Use of 32 Bit DSP
• Use of newest S? codecs
• Combination of two pieces of equipment in one
  unit

5
If you can believe that turntables outsell
guitars in Japan then you will make an educated
guess that they are gonna become the most popular
musical instrument.

• -SEE Magazine May 2001

6
Features

• Digital Audio Manipulation
• Surround Sound 6 channels of output
• Modular
• Simplify design
• New products adaptable from older versions with
  less design work
• Can create range of products with different price
  ranges
• Near Real-Time processing

7
Design Requirements
8
I/O Requirements

• Six independent of channels output
• Front L/R
• Mid L/R
• Back L/R
• Two stereo inputs (four in all)
• 47kO200pF
• 40dB gain preamp based on RIAA curve
• Headphone output

9
User Interface Requirements

• Volume change for each input channel
• Cross-fade must be fast communication between the
  fader and DSP

10
Audio System Requirements

• High quality audio processing
• 24-bits or higher of quantization
• High sampling frequency 48kHz
• Good noise characteristics
• 100SNR
• lt1 THD
• High speed for real-time processing
• Less than 50ms between fader position change and
  audio processing change
• Less than 100ms between parameter knob or button
  press and audio processing change

11
Constraints

• Complexity of system made simpler with
  evaluation board
• Learning curve
• Assembly language
• SIMD
• Fortunately, C/C compiler
• Cost of evaluation board

12
System Design
13
System Design - Overview
14
Preamplifier Module
15
Why is a Preamp necessary?

• Signal levels from record player are much lower
  than normal line level signals (up to 5mV for
  phono, up to 1 V for line level)
• Approx 40dB is needed
• Due to mechanics of sound transduction from vinyl
• Bass frequencies attenuated for ease of
  manufacture
• Equalization needed to achieve flat frequency
  spectrum amplify lows, attenuate highs (noise)
• Common feature for existing mixers

16
Design Off the shelf or from scratch?

• Answer a little from column A a little from
  column B
• Chose circuit outlined in application note for
  High Performance Audio IC, The LM833
  (http//www.national.com/an/AN/AN-346.pdf)

17
Reasons for using chosen design

• Phono preamplifiers of comparable sound quality
  are in the neighborhood of 50. Design in
  application note costs approximately 10.
• Off the shelf product would require removal
  and/or reffitting of enclosure, input/output
  connections, and power supply.
• Application Note design has documentation
  enabling the modification the performance of the
  circuit

18
Schematic of circuit
19
Circuit mechanics

• Two stage amplifier (one chip)
• Stage one Low Pass amplifier handles rolloffs
  at 50 Hz and 500 Hz
• Passive network basic low pass filter in
  sequence with high pass handles 1222 rolloff
• Stage two 10 dB gain (in this instance)

20
Simulation Performance
21
Ideal RIAA equalization curve
Note normalized to 1kHz
22
User Interface - Faders
23
Description

• Fast Interface
• Digital A/D converter AD7994
• Mechanically sound tactile device
• Alps faders for pro-audio equipment

24
Circuit
25
User Interface Microcontroller and Buttons
26
Description

• Chose PIC16F874
• 33 Lines of I/O
• SPI bus peripheral
• Fast clock speed 20MHz
• Simple to implement, already have development
  tools
• Buttons
• Tact pushbuttons, N.O.
• Debouncing circuit needed

27
Schematic
28
Button Schematic
Debouncing Circuit
29
Debouncing Circuit Simulation
Debouncing Circuit Simulation
30
User Interface CPLD and Encoder
31
Design Decisions

• CPLD- Xilinx CPLD 9536
• will implement glue logic with less cost and less
  components
• Can adapt for future products
• Encoders
• used because they can be assignable, their
  functionality is mutable
• Good speed and feel
• Digital-easy to send through communications
  interface

32
Design Overview

• Encoders will take input from user
• CPLD
• will take quadrature output from encoder
• Decide which direction
• Encode into 5 bits for all encoder functions
  using a priority encoder
• Chose XC9536 for speed, I/O, price and ease of
  implementation

33
Encoder

• 16 counts per revolution
• 90 quadrature
• Up/Dn
• Mechanical connection needs debouncing

34
CPLD
35
Encoder Debouncing Circuit
36
CPLD Logic
37
Encoder Up/Down Decision Circuit
38
Data encoding
39
Evaluation Board
40
Audio Processing
41
Processing Inputs

• Pre-amplification Outputs
• 2 independent stereo channels
• User Interface
• Effects Parameters
• Volume Levels
• Mixing Levels
• Source Positioning (Fade/Balance)

42
Effects Processing

• Order of Effects
• Saved in memory register
• Important to final output
• Parameters
• Change how each effect is applied
• Include Spatial Effects
• Output is 6 channel audio
• Specific information on each channel

43
Volume Adjustment

• Channel Volume
• Taken from volume slider for each channel
• Effects Volume
• Taken from separate effects volume knob
• Universally applied
• These are simply gain adjustments, not affecting
  the specific information on any of the 6 audio
  channels.

44
Stage 1 Mixing

• Mixes effects with original stereo audio
• Converts original audio into 6 channels to be
  mixed with the effects audio on a
  channel-to-channel basis.
• Output is 6 channel audio
• Each channel has specific information from
  effects application
• Mixing with original audio leaves effects intact

45
Source Positioning

• User-Defined Spatiality
• Adjusts speaker levels to make the source appear
  to come from one direction
• Leaves specific channel information intact, only
  changing gains on specific channels
• Based on channel fade and balance
• Calculation of Speaker Levels
• 2 dimensional vector space
• 6 base vectors for more defined distribution

46
Stage 2 Mixing

• Mixes both 6-channel audio streams
• Mixing level defined by main fader
• Output is the combined 6 channel audio with
  spatial and effect specific information
• Actual mixing has no effect on spatial and effect
  specific information aside from aural
  interference due to the inherent nature of the
  mixed audio.

47
Effects in Use

• Equalization
• Distortion
• Fade/Balance
• Delay
• Spatial Velocity
• Flanger
• Pitch Shifter
• Spatial Velocity
• Chorus
• Fade/Balance

48
Financial Budget
49
Sub Set Breakdown
50
Total Project Costs
51
Man-Power Cost Breakdown
52
Tools
53
Project Schedule
54
(No Transcript)
55
(No Transcript)
56
(No Transcript)
57
Conclusion

• Complex Project
• All have interest
• Lot of design out of the way
• Have all of the development tools
• Believe in the success of the project