This page has a good overview of the subject: Dither and ecasound | Richard's Stuffīut getting back to what I originally posted. One solution for that is to use dither, which largely cures this problem. Also, if a volume reduction factor is used that cannot be "fit" into a single bit, you also are introducing error into the signal because you must round up or down to the next bit and this introduces something that is like a low level noise component on a single bit level. When you reduce the level of the digital signal you will be eliminating information at the lowest levels of detail, the lowest bit(s). This is true no matter what format you are using. The information is already limited by the bit depth of the source. In the digital domain you have a different story. So if you want to reduce the voltage by some factor, it is not the signal that will be limiting the information content. In the analog domain the signal resolution can be considered infinite, and it is only the signal to noise ratio that is really limiting. From my engineering perspective, the problem is more about what level of degradation of the information content can be considered to be "doing no harm". But I think you need to forget about using buzzwords like "lossless" because they just do not really apply to the digital domain.
#MAC VOLUME CONTROL HOW TO#
Look, if you are looking into how to implement a high quality volume control I am all for that. I apologize for my earlier snarky post, although I have to say that the sentiment still stands for me. Here you go: objective c - Change OS X system volume programmatically - Stack Overflow
#MAC VOLUME CONTROL CODE#
you can use AudioObjectGet/SetPropertyData() and then set the volume using the properties associated - this includes controlling channels and the master channel assuming the calling code has the right privileges. This is the start (online nicer documentation): What Is Core Audio? So unless you have a separate mechanism - all the OSX integrated drivers/services and applications (ie any using the native Core Audio etc) will only work within the above limits.
#MAC VOLUME CONTROL 32 BIT#
Volume - directly is a signed 32 bit integer value, if you control using dB then it's a fixed point number (16.16bit). TRUE instructs CoreAudio to not apply a curve to the scaler representation of the volume, FALSE instructs CoreAudio to apply a curve, which is CoreAudio's default behavior. It allows you to set the scaling, including if it's linear.
In the OSX Kernel there's a class called IOAudioLevelControl. If you use a DAC with a PCM output from the Mac. So assuming a pure source (another issue) by the time the audio reaches the audio jack it's been frappe'd to oblivion. There's also the standard filters both via digital but also on the output hardware. There's perception curves in audio that I believe may also be used. Core Audio and the monolith that is OSX then performs the volume function too.
Just looking at the Xcode developer docs.įor the main part - any format is converted to PCM by OSX internally. but after truncating the intermediary samples down to 24bit for the actual DAC the resulting numbers will be identical as all the added precision is cut off.Ī different question is whether the lost resolution is audible, especially for the quiter sound. The division can be done in int32, float32, int64, float64, float128. A proper 24bit track has no volume control headroom. if you have a 24bit DAC with real resolution of 22bits, then a 16bit track has a volume control headroom of 6 bits (-36dB) to keep the original 16bit resolution. If your chain can resolve to analog domain all the lower digits created by the division, the operation is "lossless". the aforementioned CamillaDSP) start the division on samples close to zero (so called zero-crossing) and/or slowly change from the previous ratio to the new ratio (to avoid audible clicks), some handle compression close to maximum value to avoid clipping (for amplification, not attenuation), but the actual volume control is always the same. not operating an analog volume feature via some digital control channel) means simply dividing all sample values by some fixed number (or multiplying by a fixed float).
0 kommentar(er)
