I had lunch with an interesting guy who had gotten .com-money to record the whole bible professionally with good actors (in swedish and english, kjv). The idea was to sell custom made compilations of biblical texts on cd over internet. The company is now out of money (surprise!), but all the material is recorded (about 350 hours) and if anyone gets a good idea on what to use the material to, it might be possible to get permission to use it. Now to my question: how well fitted is ogg/vorbis for compressing high quality speech? I've done some limited testing with beta4 that indicates that bitrates around 64kbit/s (mono) is needed to make it sound ok. How much 'room for improvement' does the vorbis format have on that number? Would it be possible to hack a special decoder that was better at encoding and how much work would that take? I am no expert in audio compression (I'm on this list to monitor the discussions on i18n and comment encoding issues) so the answers to some/all of the above questions may be obvious. If so, please forgive me. cheers/daniel -- begin:vcard fn:Daniel Resare tel;cell:+46739442044 tel;work:+468332040 adr;work:Scheelegatan 36; 112 28; Stockholm; Sweden end:vcard pgp fingerprint: 8D97 F297 CA0D 8751 D8EB 12B6 6EA6 727F 9B8D EC2A --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
On Saturday 14 July 2001 20:03, Daniel Resare wrote:> Now to my question: how well fitted is ogg/vorbis for compressing high > quality speech? I've done some limited testing with beta4 that indicates > that bitrates around 64kbit/s (mono) is needed to make it sound ok. > How much 'room for improvement' does the vorbis format have on that number? > Would it be possible to hack a special decoder that was better at encoding > and how much work would that take?If it's supposed to be truly high quality, you can't go much lower than 64kbit/s (mono) with any codec. Maybe a couple percent. Vorbis will also improve a couple percent in this discipline in the next version. To squeeze out more it's going to take quite a lot of research and time. Note: This is not an official statement of the Vorbis project. --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
At 8:03 PM +0200 7/14/01, Daniel Resare wrote:>I had lunch with an interesting guy who had gotten .com-money to record >the whole bible professionally with good actors (in swedish and english, kjv). >The idea was to sell custom made compilations of biblical texts on cd over >internet. The company is now out of money (surprise!), but all the material >is recorded (about 350 hours) and if anyone gets a good idea on what to use >the material to, it might be possible to get permission to use it. > >Now to my question: how well fitted is ogg/vorbis for compressing high >quality speech? I've done some limited testing with beta4 that indicates >that bitrates around 64kbit/s (mono) is needed to make it sound ok. >How much 'room for improvement' does the vorbis format have on that number? >Would it be possible to hack a special decoder that was better at encoding >and how much work would that take?Speech and music are considered different problem classes by many audio codec developers. If the recording is just clear speech (ie not mixed with music intros and effects) then there are several codecs that will compress it much smaller than 64kbps and still sound OK. The GSM family is one, PureVoice (included free in QuickTime) is another, and MPEG 4 defines some new ones. With speech, the harmonic content is less important, and there is generally lots of silence that can be removed, but there is also a great deal of shaped noise in the form of sibilants (s, f, h sounds). The ear is quite sensitive to distinctions in the noise, so reducing bitrate by cutting down samplerate can sound wrong (sss turns into shhh if the HF is cut off, for example). My understanding of Vorbis is that is a general purpose compressor, and so one could make codebooks tuned for speech, but they would require some work. Based on earlier discussion here, 'noise gating' your speech first (putting it through a filter so that there is complete digital silence between words) would help Vorbis make it a lot smaller, as otehrwise Vorbis will carefully preserve the nuances of your background noise in the recording studio well below the threshold of hearing. --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.