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Bits is Bits? Right? Check Again. George Blood, Safe Sound Archive Joint Technical Symposium Oslo, Norway Monday, May 3, 2010
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Typical Playback Chain Analog source Analog-to-digital converter Digital Audio Workstation Digital File Physical Carrier of Files
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Typical Playback Chain Analog source Analog-to-digital converter Digital Audio Workstation Digital File Physical Carrier of Files }
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From ADC to Digital File ADC Digital Output (AES-3) Cable/patching/switching Digital Audio Workstation: Digital File Computer: CPU/Bus/etc. Driver Software OS/Drivers Storage interface/drivers: FW, USB, SATA, FC, iSCSI Storage Device (HDD) Interface: AES-3 to FW/USB/etc.
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Disappointments Don’t mention brands Don’t tell you our solution Very pervasive problem http://www.avpreserve.com/wp- content/uploads/2010/01/Digital_Audio_Inter stitial_Errors.pdf
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Disappointments Planned to announce a software tool to automate this testing….
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Tested Hardware Lynx AES16 M-Audio (96 and 192) M-Box Metric Halo ULN-2 Nagra V SonicStudio 302 (aka ULN2+DSP)
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Tested Software Boom Metric Halo Console ProTools LE (Mac) Sonic Solutions HDSP Sonic Studio soundBlade SoundForge WaveLab
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Tested OS Mac OS9 Mac OS X Windows 98 Windows Home Windows ME
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Tested Drivers Stock drivers (mostly) –OS stock drivers –Hardware bundled drivers Dedicated Drivers –OS 9 (Sonic Solutions) –OS X (SonicStudio & MH)
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Tested Storage Fat32 FibreChannel (2Gb, RAID5) FireWire 400 HFS+ (SCSI Ultra160) HFS-extended SATA
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Not Tested Audacity AudioCube [Bias Peak] iSCSI ProTools HD ProTools LE (PC) Pyramix RME ADC to FireWire
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Testing Multiple Components Simultaneously A b 1 A b 2 B b 1 B b 2 A a 1 A a 2
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Finding errors 100% Listen –Inefficient –Unreliable Software verification –Doesn’t certify authenticity –Limited parameter testing –Unreliable
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Finding Errors Null Test: –2 presumed identical files –Sample-accurate alignment –Invert polarity –Add together If a1=a2, then a1 - a2=0
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Aligning 2 stereo pairs (1)
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Aligning 2 stereo pairs (2)
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Aligning 2 stereo pairs (3)
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Aligning 2 stereo pairs (4)
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Aligning 2 stereo pairs (5)
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Aligning 2 stereo pairs (6)
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…then invert 1 pair
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Testing for 2 parameters Time –Number of samples Amplitude –Number of bits
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Null if mis-aligned by 1 sample
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Error of 76 samples dropped
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from: http://www.avpreserve.com/wp- content/uploads/2010/01/Digital_Audio_Interstitial_Errors.pdf
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Bits vs. samples missing 1010101010101010 1010101011101010
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Bits vs. samples missing 1010101010101010 1010101011101010
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Null if gain changed
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What happened? New Hardware –Failure Reviewed set up with engineer –Failure Reviewed old systems –Failure Simplified Test –Finally some passes –Failures continue between identically configured systems
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Qualifying a Control Round Robin Test –A≠B –B≠C –A=C –…B is wrong
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Qualifying a Control Assumes only one variable at play –Host –I/O Hardware –Driver –Application …test configuration
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Hardware in hand SonicStudio –Great editor –Semi-proprietary file types –Non-destructive editing –No support for WAV or BWF output –No AES-31 ADL support Nagra V –Simple –Self-contained –Can’t change variables (other than resolution)
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Results Null tests passed Every time Always Validates testing procedures
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Talent Pool Head of QA with physics background 2 experienced audio engineers 2 dealers 2 outside technical engineers
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Tech “support” Universally appalling Short attention span Don’t understand concepts Always some other link in chain Regional sales reps care more Engineer curious but unable to help
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Computer code “traps” Intractable problem buried in code Build routine to watch for it Applies fix Efficient solution
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Computer code “traps” Masking (aka “hiding”) problem! –Little crossfades at glitches –Other lies…
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True Nulls
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Very small error in Null
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Close up
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Incomplete Null
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Non-zero offset
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Calculating size of error “Normalize” difference signal –Increases gain to zero headroom 1 bit = ~ 6dB Normalizing amplitude divided by 6dB equals # of bits (amplitude) of difference…
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Calculating size of error 90dB / 6 dB = 15 bits
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Incomplete Null Spectrum of difference signal
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Conclusion Not passing 24 bits Truncating at 16 bits Dithering 16th - 24th bits –More noise but Lower distortion than truncating at 16 bits and dithering 17-24
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Struggling to keep up Different bit depth, all non-zero Example 3 drops samples
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Struggling to keep up Example 1 & 2 Normalized -- “properly” dithered
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“Well-dithered lie”
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Toggling single bit
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Are there no limits? “Fatter” difference on L Display higher resolution on R
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Are there no limits? “Fatter” difference on L “Full” null - absurd gain change - on R
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Are there no limits? Different residual on L!
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More absurdities Same hardware, different ages, different results Same configuration, different results on different days Same hardware, good results with one software; poor results with different software
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Conclusions Get what you pay for –More expensive hardware & software performs better in Null tests Stock drivers aren’t as good as hardware specific drivers –keep up to date, especially after OS upgrades Non-host-based systems perform significantly better Mac-based systems performed better than PC-based systems, but are far from flawless Worst PC and Worst Mac systems equally bad These problems are widely known by manufacturers and blatantly hidden
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