High Resolution Digital Audio

Review of vocabulary Prefixes: k = 1,000 Bit = 1 binary digit M = 1,000,000 G = 1,000,000,000 Bit = 1 binary digit Byte = 8 bits Bandwidth = size of a pipe through which data can flow; measured in bps (bits per second)

Sampling Rate An analog signal is “sampled” - i.e. snapshot measurements of its level at given moments in time Nyquist: you must sample at 2x the highest frequency present in the signal Nyquist limit = highest frequency you can reproduce without aliasing; equal to ½ the sample rate; You must have an antialiasing filter to attenuate frequencies above your Nyquist limit The higher your sampling rate, the higher your Nyquist limit

Bit Depth Every sample is encoded into a number Your computer uses binary numbers; Each number must be a certain number of bits long In a 16 bit system, even zero must be a 16 digit number = 0000 0000 0000 0000 Any value between bits must be quantized More bits = less error; less error = less noise Defines signal to noise & dynamic range 6 dB per bit

Sigma Delta DSD – Direct Stream Digital Different from PCM – Pulse Density Modulation Hard to work with in post – Sonoma System 1-bit converter with extremely high sample rate (2.8MHz) Low bit, high-sample rate converters are the norm Sometimes 4-bit or 8-bit “Oversampling” converter design very common Starts with high SR low bit-depth Decimated & converted to PCM 64 times 44.1 kHz (DSD64)

DXD PCM with Ultra-high sampling rates Merging Technologies Pyramix 352.8 kHz / 24-bit Merging Technologies Pyramix

Can we hear the difference? In PCM, do higher sampling rates matter? We can't “hear” above 20 kHz...

Aliasing When a frequency exceeds the Nyquist limit, it is folded back into the audible spectrum 30 kHz becomes 10 kHz If higher frequencies are not adequately attenuated, this could cause distortion or noise in the signal Anti-aliasing filters can cause artifacts of their own Higher sampling rates push Nyquist limit higher Good anti-aliasing filters make a difference

Dither Random noise applied to a signal Usually represents LSB There are many kinds of dither Can be “Noise Shaped” Suppresses correlated noise Increases dynamic range Should be applied anytime there is a conversion from higher bit depth to lower Should be the very last thing applied to your mix

Data Compression Lossy algorithms Lossless algorithms Mp3; DTS; Dolby AC-3 Perceptual coding Lossless algorithms Meridian Lossless Packing FLAC

Delivery Formats DVD-Audio: PCM Capable of 2-ch 96 kHz/24-bit Or PCM 5.1 surround sound at 44.1 kHz SACD Super Audio CD – DSD Blu-Ray 2 ch: 192 kHz/ 24-bit 5.1 surround: 96 kHz / 24-bit Also 7.1 and 9.1 Downloads No more need for a delivery format