sndfile-spectrogram: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/sndfile-spectrogram - from package: sndfile-tools

You may install the required package with command apt-get install {package}

Error in other languages:
sndfile-spectrogram: bevel nie gevind nie
sndfile-spectrogram: comandă negăsită
sndfile-spectrogram: comando não encontrado
sndfile-spectrogram: commande introuvable
sndfile-spectrogram: command not found
sndfile-spectrogram: käsku ei ole
sndfile-spectrogram: không tìm thấy lệnh
sndfile-spectrogram: komanda nerasta
sndfile-spectrogram: Kommando nicht gefunden.
sndfile-spectrogram: kommandot finns inte
sndfile-spectrogram: komut yok
sndfile-spectrogram: nie znaleziono polecenia
sndfile-spectrogram: níor aimsíodh an t-ordú
sndfile-spectrogram: no se encontró la orden
sndfile-spectrogram: no s'ha trobat l'ordre
sndfile-spectrogram: opdracht niet gevonden
sndfile-spectrogram: parancs nem található
sndfile-spectrogram: perintah tidak ditemukan
sndfile-spectrogram: príkaz nenájdený
sndfile-spectrogram: příkaz nenalezen
sndfile-spectrogram: команда не найдена
sndfile-spectrogram: командата не е открита
sndfile-spectrogram: 命令找不到
sndfile-spectrogram: コマンドが見つかりません