Sound quality

[SlawekPL]

Dear Computer Hope Forum Members,

what is the difference in audible quality between 8-bit Unsigned and 16-bit Signed PCM WAV sound besides fact, that low signal levels become disorted in conversion 16 -> 8-bit? I have done a research that 16 -> 8-bit conversion produces files easy to compress using software of choice and compressed size is not much larger than original music stored in a lossy format like MP3. In fact, a 8-bit PCM file is half a size of 16-bit PCM if not compressed using archiving software. I can hear the difference between 4-bit ADPCM and 8-bit PCM even when both have the same sampling rate: ADPCM is a lossy format. Also I've noticed no difference in sound quality between Unsigned and Signed 8-bit PCM.

I've been using Audacity to "shorten" my music and I'm impressed by how disk space is wasted by 16-bit PCM. I was wondering if can I store music converted 16-bit PCM -> 8-bit PCM practically not losing much quality of the original sound? Am I using improper computer equipment to measure sound quality? I haven't attached any sample files to this post but I'd be glad if You can do some research on Your own.

Please reply,
SlawekPL

[Geek-9pm]

To save disk space, use the ZIP tool.
Otherwise, once you have lost sound quality, you can not get it back.

Audacity can store music  files in a high quality format, but the do take more space. This is s well-documented elsewhere.
https://en.wikipedia.org/wiki/Sound_quality

The amount of space required to store PCM depends on the number of bits per sample, the number of samples per second, and the number of channels. For CD audio, this is 44,100 samples per second, 16 bits per sample, and 2 channels for stereo audio leading to 1,411,200 bits per second. However, this space can be greatly reduced using audio compression. In audio compression, audio samples are processed using an audio codec. In a lossless codec audio samples are processed without discarding information by packing repetitive or redundant samples into a more efficiently stored form. A lossless decoder then reproduces the original PCM with no change in quality. Lossless audio compression typically achieves a 30-50% reduction in file size. ...

[SlawekPL]

I'd like to stay within the WAV format and not to use archiver like ZIP.

Is there a way to minimise quality loss that can't be avoided when downgrading bit depth? For example dithering 16-bit signal so quantization error in resulting 8-bit audio is less likely to be heard:
https://en.m.wikipedia.org/wiki/Audio_bit_depth#Dither

The noise introduced by quantization error, including rounding errors and loss of precision introduced during audio processing, can be mitigated by adding a small amount of random noise, called dither, to the signal before quantizing. Dithering eliminates the granularity of quantization error, giving very low distortion, but at the expense of a slightly raised noise floor.

I need to save disk space because I want to burn a backup CD of a game that has all sound files in the Signed 16-bit WAV format. Sampling rate differs between some of files. Cutting bit depth in a half could help me to add extra content to this game that's going to be burned on a single disc.

Sincerely,
SlawekPL

[Geek-9pm]

There are different kinds of lost quality. One kind is reduction of high frequency content. If you reduce the high frequencies, less data is needed to reprocess the sound. Another kind is dynamic range. Reducing dynamic range also reduces the amount t  data. Another is reduction of accuracy. This means an increase in distortion levels.

Much depends on one's taste. The human  ear learns to tolerate the defects of recording if they do not take away the impact or meaning of the music.  Much modern music has very limited dynamic range, that that is the area where you get the greatest gain.

Not all codecs are the same. Some proprietary codecs have excellent quality and conserve space. But these are not free.

Before converting 16 bit to 8 bit, first you want to reduce the dynamic range as much as you can. This will give you materiel that does not require the full 16 bits.
However, 8 bit is very crude. You have to experiment to see  what sound s good to you. Try cutting off the high frequencies and see if you like it.

[SlawekPL]

In case of PCM only sampling rate, recording length and bit depth decides how big the file is. The sampling rate and therefore peak frequency of music that I want to "shrink" is already optimized at low value, and I could lose high frequency tones if I doubled the speed of playback to reduce time that this record plays. The last option to reduce the size of a WAV file is to reduce bit depth. PCM is "bare" digital audio that doesn't use any algorithms that makes dynamic range influence the size of a file. Otherwise I pay much attention to high-frequency sound in music that I listen to because of my sensitive ears.

I've experimented with dithering in Audacity and I've observed that rectangular or triangular dither does not allow to change bit depth of an exported WAV file as it stays in 16-bit 44.1 kHz format. No dithering at all or shaped dither yields small-sized files in the proccess of 16 -> 8-bit conversion.

Best regards,
SlawekPL

[Geek-9pm]

For reference:
For audio, dithering is done by adding noise of a level less than the least-significant bit before rounding to 16 bits. The added noise has the effect of spreading the many short-term errors across the audio spectrum as broadband noise.

[SlawekPL]

Dear Geek-9pm,
thank You for Your help and valuable information You brought to me. I think my problem is solved and my questions are answered, therefore I now understand when to save sound with 16- or 8-bit depth.

Have a good day and see you next time!