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Is adding "dither" (in 24bit) all Meridian Resolution Enhancement is?

I have no idea exactly what Meridian does, but I don't think it's a secret. That Wadia document was very complementary to the 518 manual, so I'm guessing that word length modification is simply adding random noise to the least significant bits.

I have no idea exactly what Meridian does, but I don't think it's a secret. That Wadia document was very complementary to the 518 manual, so I'm guessing that word length modification is simply adding random noise to the least significant bits.

That's a really interesting point. More MIPS (or more processing time) = more powerful filters. Take a look at the impulse responses of the following: It's 96kHz to 44.1kHz downsampling, but you can see the difference between many filter designs. Some filters pre-ring, some are Meridian-like apodizing minimum phase, a couple virtually have an identical impulse response to the impulse...

http://src.infinitewave.ca/

Dithering is a technique used to maximise the dynamic range of audio stored at a particular bit-depth: any distortion introduced by quantisation is decorrelated by adding a small amount of white noise to the signal. In most cases, SoX can determine whether the selected processing requires dither and will add it during output formatting if appropriate.

Specifically, by default, SoX automatically adds TPDF dither when the output bit-depth is less than 24 and any of the following are true:

- Bit-depth reduction has been specified explicitly using a command-line option

- The output file format supports only bit-depths lower than that of the input file format

- An effect has increased effective bit-depth within the internal processing chain

For example, adjusting volume with vol 0.25 requires two additional bits in which to losslessly store its results (since 0.25 decimal equals 0.01 binary). So if the input file bit-depth is 16, then SoX's internal representation will utilise 18 bits after processing this volume change. In order to store the output at the same depth as the input, dithering is used to remove the additional bits.

Use the -V option to see what processing SoX has automatically added; the -D option may be given to override automatic dithering. To invoke dithering manually (e.g. to select a noise-shaping curve), see the dither effect.

dither [-a] [-S|-s|-f filter]

Apply dithering to the audio. Dithering deliberately adds a small amount of noise to the signal in order to mask audible quantization effects that can occur if the output sample size is less than 24 bits. With no options, this effect will add triangular (TPDF) white noise. Noise-shaping (only for certain sample rates) can be selected with -s. With the -f option, it is possible to select a particular noise-shaping filter from the following list: lipshitz, f-weighted, modified-e-weighted, improved-e-weighted, gesemann, shibata, low-shibata, high-shibata. Note that most filter types are available only with 44100Hz sample rate. The filter types are distinguished by the following properties: audibility of noise, level of (inaudible, but in some circumstances, otherwise problematic) shaped high frequency noise, and processing speed.

See http://sox.sourceforge.net/SoX/NoiseShaping for graphs of the different noise-shaping curves.

The -S option selects a slightly `sloped' TPDF, biased towards higher frequencies. It can be used at any sampling rate but below 22k, plain TPDF is probably better, and above 37k, noise-shaped is probably better.

The -a option enables a mode where dithering (and noise-shaping if applicable) are automatically enabled only when needed. The most likely use for this is when applying fade in or out to an already dithered file, so that the redithering applies only to the faded portions. However, auto dithering is not fool-proof, so the fades should be carefully checked for any noise modulation; if this occurs, then either re-dither the whole file, or use trim, fade, and concatencate.

If the SoX global option -R option is not given, then the pseudo-random number generator used to generate the white noise will be `reseeded', i.e. the generated noise will be different between invocations.

This effect should not be followed by any other effect that affects the audio.

I guess if you generate a test wave file with nothing but a fixed frequency encoded in the lowest (say) 2 or 3 bits (of 16) then burn to CD/DVD and then play it as file or CD/DVD through M gear that internally modifies bit depth - you should get the signal on output at exactly the expected level if M res enhancement is just dithering the lower order bits in 24 after "pasting" the original 16 topside. One can compute level or rms level for specific bits allocated to the test "beat". If M res enhancement is intepolating 16 to 20 (downwards) and then adding dither in the lowest 4-5 bits of 24 then the "beat" should be at a lower bit level (lower RMS level) in the output. Might even be detectable with a simple audioband scope. I guess one couldn't confuse the beat with dither since dither (probably TPDF) is uncorrelated. I suppose someone could try that.

Even though heavy duty offline processing is possible, would you maintain a seperate library from the "Master RIP of the CD" or replace your library with the processed one?