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Topic: Wavpack bitrate? (Read 7802 times) previous topic - next topic
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Wavpack bitrate?

Hi

I'm adding wavpack support to my cd ripper. It's just about done, there's only one thing that's really confusing for me. From http://www.wavpack.com/wavpack_doc.html

Code: [Select]
 -bn = enable hybrid compression, n = 2.0 to 23.9 bits/sample, or
                                 n = 24-9600 kbits/second (kbps)


Is that really 9.6Mbps? I've never heard of an audio file with such a huge bitrate.

Any light you can shed on this will be appreciated.

For now I have one slider for the bitrate and that goes from 24 to 9600, but for obvious reasons that's very difficult to set. Should the slider range be 2-23.9 instead?

Oh and if you also know anything about this:

Quote
Although the option accepts bitrates as low as 24 kbps, the actual value that WavPack can achieve is usually much higher than that. For example, with CD-audio sampled at 44.1k the lower limit is about 196 kbps.


That is, what's the point in specifying a 24kbps bitrate if it will end up being 196?

Thanks in advance.

Wavpack bitrate?

Reply #1 –
Well even DVD-A files compress losslessly smaller than 9.6mbit but possibly if you had enough channels and the samplerate and bit depth were high enough you could have hybrid compression at 9.6mbit.  Not sure where you'd get that type of source material but it's possible.

On the other point you raised, you might be able to do hybrid compression down to 24kbps on really low samplerate mono files.  It's just CD-sourced audio (44.1kHz/16bit/2ch) that bottoms out at about 196kbps.  I'm betting the 24 mark is just where David decided to set the cutout point in the option from bits/sample to kbps.
Nero AAC 1.5.1.0: -q0.45

Wavpack bitrate?

Reply #2 –
You could make the slider offer predefined choices that would cover the huge range in non-linear fashion. But it only makes sense if your CD ripper can accept hi res multichannel audio for transcoding.

Wavpack bitrate?

Reply #3 –
If you do a search through HA you will find that for CD audio files the range that people have found to be useful is much smaller. I think I have seen recommendations in the 300 to 500 kbps range. Much below 300 and you are better off with other lossy encoders. Much above 500 and you get little audible improvement.

Wavpack bitrate?

Reply #4 –
Thanks guys, that's helpful. I'll make the range comparable to other encoders, perhaps with a higher limit.

Wavpack bitrate?

Reply #5 –
First of all, thanks for adding WavPack support to your app! 

As was said, the bitrate range is based on the possible range of input sample rates and channel number options and, in fact, the WavPack test suite located here has samples from 24 to 1024 kbps.

The 9600 kbps limit is probably a little silly, but for 7.1 at 24/192 it might make some sense, at least for the person that would record at that sample rate.

I would say that a reasonable selection for CD rips would be 256, 320, 384, 448, and 512. I don't recommend it because it generally doesn't sound very good, but some people might like 196 so that they can have the smallest possible lossy files in hybrid mode.

BTW, if you use the .dll package here your users will be able to take advantage of the dynamic noise shaping feature (--dns) once I get that into the standard release. This gives a nice quality improvement for the lossy mode files.

Cheers!

David
 

Wavpack bitrate?

Reply #6 –
Quote from: pdq on
If you do a search through HA you will find that for CD audio files the range that people have found to be useful is much smaller. I think I have seen recommendations in the 300 to 500 kbps range. Much below 300 and you are better off with other lossy encoders. Much above 500 and you get little audible improvement.


Roughly:

wavpack bitrate compare to traditional encoder:

200k --dns = 64 k
235k --dns = 120 k
270k --dns = 170 k

My perceived quality out of 10:

200k = 4.5
235k = 7.0
270k = 8.5
320k = 9.0
350k = 9.4
384k = 9.7...