Problem with audio clipping

One some models, certain audio mixer settings may result in very "harsh" and distorted sound both on the internal speakers and on headphones plug. This is especially evident when the played audio has high volume (i.e., full dynamic range).

This is caused by a hardware flaw: excessive internal amplification saturates the audio channels, resulting in clipping.

Solution: reduce the volume on the responsible mixer channel(s). e.g. in the console alsamixer with control via arrows: up/down left/right.

Model-specific observations

(you can use alsamixer panel to find out if setting to 100% amplifies anything)

• T43 (AD1981B audio controller): PCM channel volume higher than 70% may result in clipping, regardless of the Master channel.
• R40 (Intel 82801DB/DBL/DBM audio controller (AC97)): PCM volume needs to be set under 80%, higher values cause clipping. Same with the Master channel as on T43.
• R51e (AD1981B audio controller): PCM channel volume higher than 84% may result in clipping, regardless of the Master channel.
• Z61e (Intel High Definition with AD1981): Just turn down the PCM channel volume to at least 77% and you should be happy (in some combination with external speakers, 65% was needed), the Master Channel can be kept at 100%. If that doesn't help, loading snd-hda-intel with model=thinkpad and position_fix=1 might also improve a bit.
• X32 volume gain from alsamixer (gain for Line, CD, Mic, Phone, and Aux is identical as PCM)
  • Master 100% == 0dB
  • PCM 74% == 0dB
  • PCM 100% == +12dB